To provide a means for exactly, surely and stably detecting breakage of a cutting edge of a tool at a low cost.

The structure of this device is simplified by using a rotary solenoid 43 as a rotation driving source. The detecting method is also simplified by utilizing an optical sensor 59, while including a control circuit. Since the number of parts is extremely reduced, the device is manufactured at the low cost and the inexpensive device is provided. By enabling detections in right angle and horizontal directions, the device is used in various kinds of installation places.