PURPOSE: To save labor, by employing such constitution that when the degree of wear of the crushing part with the crushing ball as the center in a coal crusher reaches a critical value, an alarm is issued through a limit switch.

CONSTITUTION: In a coal crusher, an operating fluid 21 is injected into a cylinder 9a of a pressurizer 9, pressing the upper crushing wheel 8 through a piston 9c and an actuating rod 9b. When the actuating rod 9b moves downward owing to the wear of the coal crushing part with a crushing ball 10 as the center, and a pushing body 22 contacts with a switch 24, an alarm 25 is actuated. ON and OFF resulting from the rotation of the lower crushing wheel 7 are displayed on a waveform display board 26. In addition, when the wear quantity exceeds a given amount, the alarm 25 delivers a signal continuously. Because there is no need to detect the degree of wear by stopping the crusher frequently, labor can be saved.