You are correct that it is a Japanese 1 Yen coin: http://en.numista.com/catalogue/pieces1590.html
When you see these Kanji: 日本国 (Above the sappling on the obverse) you can be sure it is Japanese, or connected to Japan some how.
On the back below the "1" is the date. Japanese dates are based off the reigning emporer. You will find a date convertor for modern coinage here: http://dateconverter.net/
The date 昭'"十九年 converts to Showa year 59 or AD 1984.
When you see these Kanji: 日本国 (Above the sappling on the obverse) you can be sure it is Japanese, or connected to Japan some how.
On the back below the "1" is the date. Japanese dates are based off the reigning emporer. You will find a date convertor for modern coinage here: http://dateconverter.net/
The date 昭'"十九年 converts to Showa year 59 or AD 1984.






















