PURPOSE: To enhance the turning property of a vehicle by orienting approximately in the vertical direction of a vehicle body planes one including the axis of a crank shaft and the other that of a speed reducer shaft.

CONSTITUTION: Planes one including the axis 42a of a crank shaft 42 and others the respective axes 56a, 61a, 62a of speed reducer shafts 56, 61, 62 are each oriented approximately in the vertical direction of a vehicle and are almost rectilinear in the vertical direction of a power transmission system extending from the crank shaft 42 to the output shaft 62. Therefore the length of a power transmission is remarkably shortened in the longitudinal direction of the vehicle. In, e.g. a four-wheel buggy, the power transmission 20 is installed utilizing a vertically long space between a sheet and rear wheels, thereby shortening a wheel base to make the vehicle body compact and enhance the turning property of the vehicle.