A rotary crushing apparatus having a hydraulic motor for driving a crusher includes a load detector for detecting a loading state of the hydraulic motor, a load judging device for judging the loading state of the hydraulic motor, a feeding amount controller that stops a feeding of an object to be crushed by a feeder when the load judging device judges as overloaded or that starts the feeding of the object to be crushed by the feeder when the load judging device judges as underloaded, and a motor capacity controller that changes a capacity of a capacity-variable motor to a large capacity when the load judging device judges as overloaded. Since the capacity of the hydraulic motor is switched to the large capacity when the feeder is stopped, it is possible to crush wood in the crusher with high torque and to reduce the load in order to recover to a former state in a short time.