The invention aims at providing a fuel quantity regulating device for a diesel engine with the advantage that the fuel quantity regulation precision can be prevented from being reduced. In order to reach the goal, in the fuel quantity regulating device for the diesel engine, an engine stop operation input part is arranged on a sliding element so that an engine stop operation output part is in the opposite direction to the engine stop operation input part, when the engine needs to be stopped, the engine stop operation output part (13) is used for inputting engine stop operation force to the engine stop operation input part, then, a regulation rod is in a state of being remained at the original position, the sliding element slides in the fuel quantity reducing direction for stopping the engine, observation is carried out in a direction parallel to a quantity regulating rack pin, if a phantom line passing through the center part of a force exertion spring exists, the phantom line is used as the boundary for dividing a far-end side far from a regulating rod pivot and a near-end side near from the regulating rod pivot, and stop blocks are respectively arranged at the far-end side and the near-end side.