In a gear drive device of a railway motor car having a larger gear (24) fixed on an axle (19) and a smaller gear (23) fixed on a rotation shaft (22) of a traction motor (21), tooth trace of the smaller gear (23) or that of the larger gear (24) is twisted in a manner that the teeth (23e, 24b) of the smaller and larger gears are engaged in parallel with each other when the axle (19) is deflected due to the load of the railway motor car. <IMAGE>
