To provide an engine which can be made compact in size, and a straddle type vehicle equipped with the engine.

The engine comprises a crank case 20 which is dividedly constituted at a divided face S1 including an axial core of a crank shaft 40 and an axial core of a balancer shaft 47b, and the axial core of the balancer shaft 47b is arranged between a first horizontal face S13 including the axial core of the crank shaft 40 when the engine is mounted to the vehicle and a second horizontal face S12 including the lower end of a crank web.