Monex Group Inc. is seeking more business from Japan's growing ranks of day traders in a bid to catch up with other online brokerages.

"Even if the investor pie for Japan's stock market doesn't increase, we're going to muscle in on the huge business that competitors are doing with active traders, an area where we're weak," Monex President Oki Matsumoto said in an interview in Tokyo.

Matsumoto said he wants about 20 percent of the nation's day traders as customers within three years, but did not disclose his firm's current market share.