An unemployed man in Japan had an unexpected windfall in his mailbox when he found $10,890 in cash from an anonymous benefactor, police said.

The 61-year-old man discovered the wad of cash last week along with a slip of paper with the message, "Please make use of this in your everyday life," written with a black ballpoint pen.

But instead of following the advice, the jobless man in the ancient capital of Nara in western Japan turned over the gift to police.

The sender has until June 27 to claim the money or the unemployed man will get it.

Along with the letter, the envelope contained a partial photocopy of a map of nearby Osaka without any address marked or further explanation.

"He has absolutely no clue who it is," a police official said.

Japan has seen a string of cases in which large sums of cash have been left anonymously in people's mailboxes or public toilets.

The largest single drop-off so far was in the city of Kyoto last year, astonishing a 67-year-old woman who found an envelope containing $108,900 of stacked bills in her mailbox.