Dont know who the other 5 guys are but this is a big clue found by nhbenz. Meiji Centenary?
Stamps, Coins and Banknotes Auctions
View attachment 1182153
The additional information here confirms what I translated before. Besides the description of the medals in English, note the six large characters on the lid. From right to left (!) the last four are the same four characters on the obverse of the medal we are investigating. The leading characters, 記念, depending on how they are grouped with the third and fourth (百年記念) either expand the translation to "hundred years commemorative" or reduce it to simply "centennial". As to the trailing characters, 明洽, I was conflicted as to whether I saw them correctly since they are stylized in the font on the original medal, but after seeing what Bigcypresshunter posted, I see the error:
I goofed one tiny stroke in a radical of one character. The correct characters are thus: 明治百年記念.
Together, that phrase translates to "Meiji Centennial".
Now we only need to find the specific example.
Edit: Think I got it.
http://www.nozakicoin.jp/index.php?main_page=product_info&products_id=1095
Edit: Here's a good resolution picture of your reverse on the left, albeit branded 1968.
Edit: Here you go. Definitely it, just a 1968 stamping. This is the second site which has stated the coin is silver and weighs 40 grams, first one to provide measurement of 40 mm diameter. Now recalling that everything is super expensive in Japan, this person is asking for 15000 yen which is about $120.
http://page13.auctions.yahoo.co.jp/jp/auction/r129780980
