行政主任既英文名係咩?

They are just the same, both names are fine.

Both names are used because they mean the same thing.


Its just administration is noun and administrative is adjective.
An officer responsible for administration duties, or an officer which is administrative in nature. They mean the same thing basically.

行政主任應該係 Administrative Officer, Administration Officer 錯Gammer...

如果Administration Officer 即係用錯字眼

Adminitrative Officer 才對.
因Administrative 是adjective 解 行政的.....
Adminitration 是Noun 解 行政