PURPOSE: To enhance the starting characteristics of a diesel engine by assembling an auxiliary piston with a timer piston for determining the injection timing in a distribution type fuel injection pump for the diesel engine to thereby automatically advance the injection timing at starting time.

CONSTITUTION: Fuel is fed under pressure through a fuel pump 2 and a pressure control valve 5 into the chamber 4 in a fuel injection pump 3. A pump and distribution plunger 7 is disposed integrally with a cam disk 8 making contact with a roller holder 9 within the pump 3 to thereby supply fuel through a passage 17 to a nozzle (not shown) by means of the rotation and elevational movements thereof. A timer piston 23 is connected through a rod 22 to the roller holder 9. Further, a check valve 38 and an auxiliary piston 30 forming a chamber 31 make contact with the piston 23. When hydraulic pressure operating the hydraulic chamber 26 becomes higher than predetermined value, it exhausts the air in the chamber 31 to fasten the movements of the piston 23.