* Investors caution against steep rise - fund * FamilyMart tumbles on poor forecast By Ayai Tomisawa TOKYO, April 10 (Reuters) - Japan's Nikkei share average rose on Wednesday, moving closer to a near five-year high, helped by ongoing optimism in the economic outlook since the Bank of Japan started its sweeping monetary expansion campaign, lifting real estate stocks and banks. Overnight gains on Wall Street also underpinned Japanese equities, though gains may be capped in late trade with investors cautious of signs the market is overbought after the Nikkei's sharp rise in the past week. The Nikkei gained 1.0 percent to 13,319.11 at mid-morning trade, moving closer to an intraday high of 13,331.39 the previous day, its highest level since August 2008. The index currently trades 6.4 percent above its 25-day moving average of 12,464.24. A level above 5 percent is considered overbought. "The market has been gaining sharply, especially reflationary stocks. The rises have been very, very steep," said Yasuo Sakuma, portfolio manager of Bayview Asset Management, adding he would not be surprised if investors wanted to lock in some of their gains. Analysts said that although the mood remains positive, the rate at which the index climbs tends to slow when it trades above 13,200. Asset-related stocks outperformed the market, with Mitsui Fudosan Co rising 2.2 percent and Mitsubishi Estate Co gaining 2.8 percent. Banks also attracted buying, with Mitsubishi UFJ Financial Group soaring 3.9 percent and Mizuho Financial Group gaining 2.8 percent. However, FamilyMart Co nosedived 7.9 percent after the convenience store operator's worse-than-expected earnings forecast for the year through February 2014 disappointed investors. The broader Topix 1.5 percent to 1,118.43. The Nikkei has gained more than 5 percent since Thursday's BOJ announcement of massive monetary stimulus. The central bank plans to inject about $1.4 trillion into the economy in less than two years by buying government bonds across the yield curve as well as riskier exchange-traded funds (ETFs). The benchmark has surged more than 50 percent since mid-November, when Shinzo Abe promised expansionist fiscal and monetary policies, dubbed "Abenomics", to revive Japan's economy during his election campaign. He was elected prime minister the following month.