The worst-ever start to a year for stock markets and oil's historic slump have not deterred Japan's postal savings bank, which is preparing to shift more of its $1.8 trillion portfolio into equities and alternative assets.

Japan Post Bank Co. will start investing in shares directly within a year, Katsunori Sago, who oversees the portfolio, said Wednesday in an interview in Tokyo.

Sago also said he wants to put "several trillion yen" into alternative assets such as private equity and hedge funds over the next five to 10 years.