It is Chinese, not Japanese. A student's ruler, not military, as can be read from the info printed on it.
Nick, many thanks for your answer!
You helped me a lot.
Best regards, Michael
soldiers have been known to bring back some very odd souvenirs.
LIFE'S LOSERS NEVER LEARN FROM THE ERROR OF THEIR WAYS.
Today I was talking with a friend, who is now in this ruler. He told me that grandfather brought a ruler for his children, he thought that after the war, they do not have school supplies. He also brought a aluminum soldier canteen, but for himself.