It is very important to know how to apologize in Japanese, as its kind of custom or polite to apologize even if its not your fault.You can say 'ごめんなさい' This is pronounced as 'gomen nasai', or you can simply say'ごめん' (gomen) if the situation is between friends.すみません(sumi masen) can also be used when you want to make an apology. It can also be used when you want to say 'excuse me'.