Japan Post Bank Co. said Wednesday its first-half profit rose about 20 percent on increased returns from bond investments, including government debt.

Net income rose to ¥372.6 billion for the six months to Sept. 30, from ¥309.2 billion a year earlier, the Tokyo-based company said. Post Bank, independent since October when the postal system was privatized and split into three parts, has about ¥181 trillion in deposits, the most in the world.

Post Bank's earnings dwarf those of Japan's biggest publicly traded banking groups. Combined first-half profit at the six biggest, led by Mitsubishi UFJ Financial Group Inc., fell by about half to ¥947.9 billion, partly because of losses on securities linked to subprime U.S. mortgages.

Mitsubishi UFJ said in November its net income dropped 50 percent to ¥256.7 billion in the first half. Profit slid 17 percent at Mizuho Financial Group Inc. as it posted a ¥70 billion subprime-related loss.