Share prices soared today on the Tokyo Stock Exchange, pushing its main price index to a new high while the U.S. dollar lost ground against the Japanese yen. The Nikkei Stock Average of 225 selected issues, the most widely followed price index of the exchange, gained 323.15 points, or 1.15 percent, to close at 28,489.57. The dollar closed at 123.70 yen, after opening at 123.80 yen and moving in a range of 123.63-123.88 yen. Thursday's close was 124.10 yen. Securities dealers said the Nikkei index's strong showing was a reflection of bullish sentiment prevailing in the market. ``There is no outstanding factor which is pushing share prices up,'' said Keiichi Nishida, a dealer at Kidder Peabody's Tokyo office. ``Most investors are feeling it is about time share prices should start picking up. I think we can say the market is turning bullish.'' Nishida said the strong performance of financial and food shares ignited the market bullishness across the board. In the currency market, dealers said general sentiment toward the dollar remained bearish, but investor anxiety about intervention by the Bank of Japan was holding up the currency. ``It is unlikely that the dollar will go below 123.50 today because the Bank of Japan is likely to intervene,'' said an exchange dealer at a U.S. bank in Tokyo. The Bank of Japan reportedly has been buying dollars intermittently in recent sessions to help keep the currency from falling further.