How do you say I'm sorry in Japanese?

You may say 'sumimasen' to apologize if something you are doing is inconveniencing someone. (In this way, it is similar to 'Excuse me.' If you bump into someone, you can say 'sumimasen' to apologize. It can also carry the meaning of 'thank you;' you may say it, for example, if someone serves you something.)

Other methods of apologizing are; 'Gomennasai,' 'gomen ne,' and the very polite 'moushi wake arimasen [deshita].' Meaning "I have excuse," it can be used to apologize for bigger transgressions.