兌換率-會計問題...急急急...15分

這個內部兌換價與銀行牌價的差別你可以記入“兌換收益”，如果這個收益不是因trading引起的，在計算利得稅時是不用交稅的。
當然，你公司內定的兌換率只是方便平時記賬用的，在年底時如果與銀行公布的實際兌換率相差太大的話，應作相應調整。

That is common there are many references of exchange rates. In your case, you can use your internal pre-set exchange rate to converse the JPY into HKD. There may have the exchange gain, and such exchange gain will go to the Profit and Loss A/C. As this exchange difference is not realised yet, this should not be taxable. You are able to add back such exchange gain in your Profits Tax Computation. Also, the IRD has its reference of exchange rate for many currencies, and you may use such exchange rate for your internal reference in order to easy prepare the Profits Tax Computation.