To prevent a breakage of the hydraulic motor or the power transmission member of the crusher when the crusher is overloaded owing to an excessive hardness of an object material or impure components in the material, e.g. large reinforcment or steel frames.

A controller 23 has a pressure sensor detecting the driving pressure of the hydraulic motor 15 for the crusher and controls the speed of the hydraulic motor. The controller 23 judges the overload of the crusher on the basis of the driving pressure of the hydraulic motor 15 detected by the pressure sensor. When judged to be overloaded, the controller 23 carries out an overload speed reduction control to reduce the speed of the hydraulic motor 15.