In order to determine contact erosion of an electromagnetic switching device, a mechanical parameter is measured which characterizes the time course of the relative movement between the contacts, said movement being caused by an actuator. The point in time when the contacts close is determined by evaluating the time course of the relative movement, and the distance traveled by the contact/s until said point in time or the distance traveled by the actuator from said point in time until reaching the final position thereof is detected at least indirectly and is compared to a stored reference value.