An apparatus for preventing cavitation damage to a diesel engine fuel injection pump comprises a valve member mounted on a barrel port to shut the barrel port during an early stage of fuel compression performed by the upward movement of a plunger to increase the pressure in the barrel port, a valve housing installed in the deflector or the barrel of a pump housing to support the valve member, and a pressure control valve constituted by a spring interposed between the valve member and the valve housing to elastically support the valve member. The barrel port is shut to increase the pressure therein during the early stage of fuel compression, and when the pressure of fuel in the barrel port exceeds a level higher than an open level, the barrel port opens to discharge fuel.