To provide a drill breakage detecting device to form a pressure foot device in a compact manner.

A sensor 51 provided with a projection head 52 and a receiving head 53 is mounted on the outer peripheral wall on the front side of a pressure foot 20. A mirror 57 is mounted below the sensor 51. The mirror 57 is mounted such that irradiation light irradiated in a down state is changed obliquely downward by a reflection surface 58 and brought into a gentle angle approximately equal to a horizontal and irradiated to a drill and reflection light reflected obliquely upward at a gentle angle approximately equal to a horizontal by the drill is changed into an up state by the reflection surface 58 and enters a receiving head 55. Irradiation light reflected by the reflection surface 58 and reflection light returned to the reflection surface 58 pass through one groove space S of an air inflow groove 42.