有一間公司　買左另一間公司　３０％　股份　(unlisted shares)

As $4.0 million on acquiring the shares of the company, this cost has to be debited to Interest in Associates account (Investment in Associated Company account). The excess $1.0 million maybe regarded as the goodwill and no need to segregate it from the total cost.
In each financial year end, the valuation of this investment has to be assessed, say the net assets value of the Associate, to see whether impairment, if any, be adjusted in the Interest in Associates account. If there is a reduction in value, this amount will be credited to Interest in Associates and debited to Impairment on Investment account which will be reflected in profit or loss.