An internal combustion engine, in particular a Diesel engine, includes an injection pump with a filling ramp and a supply ramp of a cam ring, cam disk or cam shaft, pump pistons traveling on the filling and supply ramps, and a magnet valve controlling the injection pump and having a closure defining a supply onset. An apparatus for ascertaining at least one actual operating state of the injection pump includes a structure-borne-sound transducer ascertaining at least one actual operating state.