The invention relates to a speed change gear drive for a transmission that can miniaturize an engine by improving the layout of parts. In particular, the invention relates to a speed change gear drive in which a change spindle is supported by a transmission case and a shift drum supported by the transmission case so that the shift drum can be rotated is driven by the turning of a change arm fixed to the change spindle, a shift fork the position of which is changed by the rotation of the shift drum and a shift fork rod that supports this shift fork are provided, and the change spindle and the shift fork rod are overlapped when the body of an engine is viewed from the side.