A power unit for a small type vehicle wherein a speed change mechanism is disposed on a lateral side of a crankcase on the side of one end of a crankshaft. A valve operation controller for controlling the operations of valve operation mode change mechanisms and a speed change controller for controlling a speed change operation of a speed change mechanism are attached to an engine body, to lay out the valve operation controller and the speed change controller in good balance of center of gravity so as to prevent the center of gravity of the power unit from being deviated to one side. The valve operation controller and the speed change controller being attached to the engine body on the opposite side of the clutch device with respect to a vehicle body center line in a direction along the axis of the crankshaft.