Engine and straddle type vehicle

An engine of the invention includes a crankshaft including a crank web; a clutch shaft disposed behind the crankshaft and provided with a clutch; a balancer shaft disposed in front of the crankshaft and provided with a balancer weight; a crankcase for accommodating the crankshaft, the balancer shaft and the clutch shaft; a cylinder section attached to the crankcase; and a starter motor disposed above the cylinder section and capable of driving the crankshaft, wherein the balancer shaft is disposed between a first horizontal surface intersecting an axial center of the crankshaft when the engine is mounted on a vehicle and a second horizontal surface intersecting a lower end of the crank web when the engine is mounted on the vehicle, the balancer weight is disposed below the first horizontal surface, and the starter motor is disposed forward of a vertical surface intersecting the axial center of the crankshaft when the engine is mounted on the vehicle.