To surely prevent a crusher from being damaged by overload by detecting the level of a raw material in a crushing chamber therefor in an engine driving type gyratory crusher and detecting the number of revolutions in the rotary driving shaft of the crusher and stopping operation of the crusher in accordance with the detection result.

In the case of producing crushed sand, a raw material in a hopper 10 therefor is segmented by a vibrating feeder 20 and supplied to an engine driving type gyratory crusher 40E. The raw material after crushing is sifted by a vibrating screen 60 and on one side, an oversize product is returned to the gyratory crusher through a transport route. In this case, the output shaft of an engine is connected to the rotary driving shaft 7 of the crusher 40E so as to be freely joined and interrupted by a clutch 240. Further, a level instrument for detecting the level of the raw material is provided in the raw material crushing chamber of the crusher 40E and a tachometer 40b is equipped which measures the number of rotations of the rotary driving shaft 7. When the level of the raw material continues the upper limit set value for constant time and exceeds it, operation of the crusher 40E is stopped by a controlling device according to these output signals.