Why does Jesus call himself 'son of man' ?

Because God the Father sent Him to Earth in human form, being born to a human mother. "Man" in this case simply means "humanity".

He is fully man and fully God. This was the result of the Incarnation. When God became a mortal man. 

God was his Father (Son of God), and Mary was his mother (Son of man). 


The Hebrew word adam lowercase means man, mankind. Jesus descended from Adam through Mary making him Son of man (adam).


>>>>If he is also 'son of god', wouldn't that imply that god is also a man?


No. God is Spirit, not flesh and blood. Scripture calls Jesus "God in human flesh"


1 Timothy 3:16 KJV — And without controversy great is the mystery of godliness: God was manifest in the flesh, justified in the Spirit, seen of angels, preached unto the Gentiles, believed on in the world, received up into glory.

Jesus often referred to himself as the Son of man. Matt 8:20 This expression shows not only that he was fully human but also that he was the son of man referred to in Bible prophecy.  Daniel 7:13, 14

He thus showed that he was neither a materialized angel nor an incarnation. Rather, he was fully human.

 By his holy spirit, God transferred his Son’s life from heaven to earth, causing conception in the womb of the virgin girl Mary. 

By identifying himself this way, he highlighted his human birth the fact that he was truly a man. Thus he also revealed himself to be that son of man whom Daniel had seen in vision appearing before Almighty God.

When Jesus applied this term to himself he was a human, so he was literally a son of man.

 He also gave his life to ransom humans, thus acting out the role of mankind’s closest relative truly a “Son of man.” Matt 20:28

Son of man is an 
expression found about 80 times in the Gospels. It applies to Jesus Christ and shows that by means of his fleshly birth, he became a human and was not simply a spirit creature with a materialized body. The phrase also indicates that Jesus would fulfill the prophecy recorded at Daniel 7:13, 14. In the Hebrew Scriptures, this expression was used for Ezekiel and Daniel, highlighting the difference between these mortal spokesmen and the divine Originator of their message.​—Eze 3:17; Da 8:17; Mt 19:28; 20:28.

"Son of man" is an expression that means Jesus, a human being, a man in the flesh.

In the Reina-Valera (Spanish Protestant) Bible, Christ calls himself the Son of The Man, or the son of God.

Jesus refers to himself as the "son of man" over 400 times in the gospels.  That phrase is found throughout the Old Testament and simply referred to one who was in position of service and obedience to God.  It is not a reference to the physical nature of the person.  It is a reference to their role.

Interestingly you will also not find a single place in the gospels where Jesus refers to himself as "the Son of God."  There are six times where other people do apply that title to Jesus.  And in five of the six times it states that phrase was intended to be statement that they believed Jesus to be divine.

The apostle Paul explains it in Philippians 2:5-11.  There he quotes what is the old known creed (statement of beliefs) of the Christian church, a statement that predates the teachings of Jesus.  In it he states that Jesus is the same as God.  But that he set aside that role for a time, took on the role of a servant and was made in the form of a human.  He became "the son of man."  He became someone who served and obeyed God.  Even to the point of his death.

During the time of his public ministry Jesus did not claim to be God.  Because at that time he was not acting in the role.  He did claim that he had been god - such as when he talking about how he and Abraham had known each other 1800 years before.  And he talked about how he was be God in the future - such as his statement to the high priest that they would see him seated on the throne of heaven.  But during his earthly ministry he limited himself to the role of servant - a "son of man."

Because of that, Paul goes on to say, Jesus was raised up from the tomb and returned to heaven. There he is now seated on the throne of heaven, and every knee is required to bow to him as Lord.

Yes, it does mean that God took on human form.  It had to be a human who redeemed mankind.  God was unwilling to have any one else die for the salvation of mankind.  So he took on human form and did it himself.  

because he didnt actually know who is father was/

There's no good evidence that Jesus was referring to himself in those passages.  That seems to be a later interpretation.  The phrase "son of man" was used often in Hebrew writings and had various meanings.  None of them were taken as messianic prophecies.