An engine for vehicle includes an oil hydraulic automatic transmission for changing the change gear ratio by control of an oil pressure. The oil pressure control unit of the transmission includes a plurality of control valves for controlling the oil pressure, and is mounted to an upper portion of a crankcase. A power transmission shaft interlockedly connected to a counter shaft and having an axis parallel to the counter shaft is disposed on the lower rear side of the counter shaft, and a drive bevel gear on the power transmission shaft and a driven bevel gear are meshed with each other on the rear side of the axis of the power transmission shaft. The resulting configuration eliminates the need for a special measure to protect the oil pressure control unit, and prevents interference of the driven bevel gear with the gear speed change mechanism.