Cover Letter Guidelines
Japanese generally do not write cover letters when they are applying for a job, but including a simple letter in both English and Japanese, addressed to the person who is receiving it, is a nice gesture.
When writing in Japanese, the text sample below can be used (an exact translation follows the sample). However, using a complete Japanese application will set very high expectations in regards to the candidate’s language skills. The letter sample uses the polite Japanese language (keigo), which is difficult for even native Japanese speakers to master. Japanese usually prefer a more humble approach and a more modest portrayal of one's abilities. If one begins by using high-level Japanese, it will be expected to continue.
In Japan, the official language is Japanese, but English is the primary foreign language and is taught in schools and used in some businesses. However, one should not assume that the recipient of an application can read fluent English. Keeping the content simple and using short sentences will make it easier for an HR manager to understand and respond. When applying for a job which has been advertised in English, a brief letter and résumé in English would be appropriate, unless the ad is asking for specific languages.
Any company in Japan, either foreign or Japanese actively looking for a foreigner, will happily accept a US style resume in simple English. In addition, including a Japanese rirekisho (see below) or a translation of the resume into Japanese, along with a photograph, is very appropriate.
Two different types of rirekisho exist; together they present the content of a typical English résumé:
Rirekisho: a Japanese résumé, consisting of two pages with basic information and a brief work history.
Shokumu-keirekisho: work history mainly used by technical professionals.
A majority of Japanese job applicants submit both rirekisho and shokumu-keirekisho.
You'll find more advice and cover letter and resume samples in the complete Japan Guide.