Handshake or bow, never both
When conducting international business with international businessmen in Japan, you have two choices when greeting them: shake their hand or bow to them. Either one is acceptable, but we recommend you follow the cue of either your guide or the Japanese businessman. Nothing can be more awkward than sticking your hand out to their bowed head.
However, it doesn’t really matter which one you do, as long as you don’t do both. It’s not that it’s against the law or anything, but bowing and shaking hands is just redundant. But if you really want to make a good first impression, you should bow down slightly as you greet them.