A fuel injection pump prevents the uninterrupted supply of fuel through an orifice to a cam chamber. An orifice inlet is formed on the same plane as a wall surface of a discharge fuel chamber. As a result, foreign substances, which are carried with the flow of the fuel to the vicinity of the orifice inlet, will fall downward in the discharge fuel chamber to a location away from the orifice inlet thereby preventing the foreign substances from residing in the vicinity of the orifice inlet, as occurs in the case of a conventional fuel injection pump. Specifically, since the foreign substances residing in the vicinity of the orifice inlet can be removed at each engine stop, the amount of foreign substances collected in the vicinity of the orifice inlet can be prevented from increasing during engine operation.