can a Hong Kong product be used in Europe

Japan uses 100 volt for most audio equipment at 60hz.

Of course Hong Kong is in China but you can get a voltage convertor.

Japan is 100V, some of the country is 50Hz, some is 60 Hz.

Hong Kong uses 200/220V 50Hz.

hmm,, here we have 220-240v. 50-60hrtz. so i guess i can use a HOng Kong amp here then..

You don't say where you are but you don't have 50-60Hz.

You have either 50 or 60 Hz.

The voltage is not that big of an issue (200 vs 220 vs 240) but some devices will not work correctly if the Hertz aren't correct. That is less of an issue as we become more universal and devices are designed for a global market but it can be an issue so you need to know. I suspect you are 50Hz if in Europe and that is the same as Hong Kong.