The invention prevents reverse rotation of a diesel engine which is possible to occur when the engine is started. A camshaft 13 is driven by a crankshaft 5 through power transmission means, and cams 14, 21 and 22 are provided on camshaft 13 so as to drive a fuel injection pump 12, an intake valve and an exhaust valve, respectively. In fuel injection pump cam 14, middle stage portion 53 is radially larger than minimum radius portion 51 and is disposed at a predetermined angle R3 on the back side in the rotation direction of the fuel injection pump cam from maximum radius portion 52.