Softbank Corp, Japan's smallest cellphone operator, aims to raise the number of its third-generation base stations to more than 50,000 next year, President Masayoshi Son told a group of reporters on Monday.

That would be at least a 6.4 percent increase from the 47,000 base stations, which connect cellphones to phone networks, that it had as of the end of September. Son, Softbank's founder, did not give an investment figure.

We are aiming for the high 50,000s, said Son, who made billions by investing in Internet ventures like Yahoo Inc in the U.S. We are working harder than promised.

Softbank is battling for market share with bigger rivals NTT DoCoMo Inc and KDDI Corp, but it has fallen months behind its schedule for setting up base stations, slowing the expansion of its service area.

Still, it has outpaced both DoCoMo and KDDI in netting new sign-ups with its low-cost price plans and a marketing blitz, luring users away from DoCoMo, which controls more than half of Japan's mobile phone service market.

Shares of Softbank were up 2.3 percent at 2,455 yen at 0435 GMT against a 2.7 percent rise in the benchmark Nikkei average.

Softbank, which bought Vodafone's Japan unit in April last year, competes with consortiums led by DoCoMo and KDDI and also with Carlyle-controlled handy-phone firm Willcom Inc for licenses to supply high-speed Wireless Internet access.

Saddled with debt of $12 billion after the Vodafone buy, Son's firm has cut salaries and changed the way it sells handsets to avoid paying commission to retailers.

Both DoCoMo and KDDI have since cut their basic fees and have said they mean to gradually cut commission paid to mobile phone vendors to offer lower price plans.

But Softbank, which has pledged to match price cuts by rivals, is not launching further price cuts, since its White price plan remains competitive, said Son.

Softbank, which plans to spend 387.9 billion yen in the year to March on base stations and networks for its wireless business, sees its mobile phones as a core part of its group, which includes Yahoo Japan and baseball team Fukuoka Softbank Hawks.

Softbank, which holds a 33 percent stake in the parent of Chinese e-commerce firm, is eyeing further investments in Internet start-ups around the world, Son said.

(Additional reporting by Mayumi Negishi; Editing by Malcolm Whittaker)