An engine is constructed such that respective centers of gravity of a crank shaft, a balancer shaft and a cylinder are positioned close to one another and the mass of the engine is thus centralized. The engine includes a shaft center of a cylinder that is offset to one side with respect to a shaft center of a crank shaft, and a balancer shaft is disposed on a side of the engine where the cylinder shaft center is offset with respect to a first parallel line which intersects with the crank shaft center and extends substantially parallel to the cylinder shaft center.