A self-propelled crushing machine is provided which ensures that, even when crushed pieces of an object include a concrete reinforcing steel bar or other like material piece, it is prevented that the concrete reinforcing steel bar will pierce into a conveyor belt. To this end, the crushing machine has a memory for storing a relationship in belt velocities between a conveyor belt and a magnetic separator belt which relationship allows a concrete reinforcing steel bar attracted and adhered to the magnetic separator belt to be taken off of the conveyor belt before the trailing end of the concrete reinforcing steel bar travels past a leading end attraction/adhesion position at which the leading end of the concrete reinforcing steel bar is to be attracted and adhered to the magnetic separator belt. In addition, the crushing machine also includes a controller configured to provide respective control currents to a conveyor belt drive means and a magnetic separator belt drive means, based on the belt velocity relationship stored in the memory.