An electromagnetic actuator for a valve mechanism, in particular in a common rail system of a motor vehicle, comprising an armature tappet for actuating a valve element located in a channel, and comprising a pole core, the armature tappet being movable axially along a central axis of the actuator when an excitation coil of an excitation system is energized. The pole core therefore has a tubular shape and has a circumferential flange in the area of the pole core end facing the channel, said flange extending inward in relation to the central axis.