I’m sorry about all the fuss.
As you might expect in a language that offers so many occasions for apology, there are many different ways to apologize. Just which way is appropriate in a given situation depends on a number of factors, the first of which is the identity of the person you’re apologizing to. For example, take the familiar form
This is a perfectly appropriate way to apologize to someone in your family, a close friend, or a child. It would be a serious breach of etiquette and imply a lack of common sense, however, to use this form with one of your elders or a superior at work. In that case you would probably best be advised to say:
Moushiwake arimasen deshita.
Please accept my apologies.
If you make a mistake at work or somehow cause trouble for someone who is not part of your immediate circle, this type of apology will probably be appropriate. Later, once the dust has settled and the mistake has been rectified or the trouble resolved, you’ll probably have an opportunity to say you’re sorry once again—to perform a sort of follow-up apology. For that purpose, the form at the beginning of this section, osawagase itashimashita, is an excellent choice.
Let’s compare osawagase itashimashita with a similar form that is often used in the same way:
Gomeiwaku o okake shimashita.
I apologize for causing you so much trouble.
Either form could be used for a follow-up apology. Generally speaking, though, osawagase itashimashita tends to be used when there really wasn’t too much harm done or serious trouble caused in the first place. Gomeiwaku o okake shimashita, on the other hand, is more often used when the original matter was serious enough to possibly have a more lasting impact—when the water might not have all flowed under the bridge yet. Thus, you might consider three grades of apologies for circumstances like these: the first and most weighty is moushiwake arimasen deshita; the second, not quite so grave, is gomeiwaku o okake shimashita; and the third and least somber is osawagase itashimashita. It’s probably safe to use the latter expression if the person you’re apologizing to seems glad to put the incident behind her. If you’re lucky, your apology may even draw a smile.
– Source: A handbook of common Japanese phrases –