An engine includes an angular velocity detecting means 10 for detecting a rotation angular velocity of a crankshaft 11 of the engine, a torque generated by the engine detecting means for detecting a variability of the angular velocity amplitude obtained by the angular velocity detecting means 10 as the variability of the torque generated by the engine. The engine compensates a fuel injection quantity by comparing the angular velocity amplitude detected by the angular velocity detecting means with the adequate angular velocity amplitude.