Convenience store chain operator FamilyMart Co. has announced that smaller rival am/pm Japan Co. has become its wholly owned subsidiary.

The effective cost for the acquisition was about ¥12 billion, with FamilyMart buying all 170 shares in am/pm Japan for ¥1 and outstanding loan assets from Rex Holdings Co., am/pm Japan's parent firm, at book value.

Through the transaction, third-ranked FamilyMart and am/pm Japan, No. 7 in the industry, will have a combined total of around 8,700 stores in Japan.