Tokyo, July 17 (BridgeNews) - Japan's index of leading indicators, which shows economic conditions two to six months ahead, was revised up to 77.8 in May from a preliminary 71.4, the Economic and Social Research Institute at the Cabinet Office announced. The leading index was above the critical 50.0 "boom - r-bust" level after it was below the level for the previous four consecutive months. An index below 50.0 signals economic contraction, while that above the level indicates economic expansion.