How to turn down a job offer

Question

I recently received a job offer from a company, say X会社. However, I would like to turn down their offer as I have some opportunity at my current place of employment.

How can I express this in a polite manner as to not offend them ?

After a few searches it seems that:

体{てい}よく断{ことわ}る

Is the polite expression to decline an offer. Is what I am looking for, i.e. "Declining politely". I found a website with a number of phrases, however, I am not sure which to choose and how to use them in my case. I would like to explain something along the lines of:

Thank you very much for this very interesting offer. However, due to an opportunity at my current place of employment, I have to refuse your offer. I am sorry for the trouble I may have caused, and hope to maybe work with you at X in the future.

Although I think I can get around the first part with something along the lines of:

就職｛しゅうしょく｝の機会｛きかい｝を与｛あた｝えて誠｛まこと｝にありがとうございます。

I also have ideas for the last part, around using 手数, but I would really need some help for the refusal itself.

I guess proper keigo would be the only acceptable level of speech, but as my Japanese is not so good, I would like to keep it as natural as possible for someone my level (JLPT N3).

Answer 1

If you're really grateful for the offer, and you'd like to stay in touch with X会社, but you can't help but turning it down, then you can't be too polite. You could write something like this:

非常に魅力的なご提案をいただき、ありがとうございます。○○様に誘っていただいたことを大変光栄に思っています。
しかしながら、現在の職場でどうしても責任をもって終わらせたい仕事が残っているため、大変残念ですが、今回はご期待に沿うことができません。申し訳ございません。
今後も○○様ご一緒にお仕事をさせて頂くことがあるかもしれませんが、その時はどうぞよろしくお願い致します。
最後になりますが、○○様のますますのご活躍をお祈り申し上げます。

If you're not particularly interested in the job offered, and you just don't want to be too rude, try something like this:

ご提案ありがとうございます。せっかくのお申し出ですが、残念ながら今回はお断りさせていただきたいと思います。あしからずご了承ください。御社のますますのご発展をお祈り申し上げます。

With this simple mail, I think the person in X会社 will realize your position, and probably wouldn't try to headhunt you again.

As @broccoliforest said in his comment, saying 体よく断ります is out of the question.

You can say 「○○の機会を与えてくださりありがとうございます」, but using 就職 would sound still awkward to me, because you're already employed by another company. Instead, you can say 「転職の機会を…」

(I'm not a keigo master, so any suggestion to improve this is appreciated.)