Atertiary negative deviated flexing contact type gear drive as set forth in claim 1, characterized in that tooth flank of the both gears (2, 3) are defined by a composite tooth profile including a straight line (MF) and a concave curve which is symmetrical to the tooth profile of each of the tooth faces of the gars (2, 3) with respect to each of the datum points (M) of tooth profiles of the gears (2, 3), or the tooth flanks of the both gears (2, 3) are defined by a so tooth profile which is obtained by providing the composite tooth profile with a certain amount of escape.