To provide a machining monitoring device for a machining apparatus that can detect a deteriorated state before breaking of a machining blade such as a drill, can monitor whether or not the machined state is good, and can be easily installed.

The machining apparatus is used for forming holes in a printed board 14 with a drill 12 repeating a unit machining operation. The machining apparatus comprises a duct 15 that sucks cut chips 19 of a workpiece which has been machined, a light source 22 that radiates light into the duct, a photoreceiver 23 installed at a position through which the radiated light is passed and introduced, and a signal processor 25 comprising a means for detecting a change in output voltage of the photoreceiver 23 caused by the passage of the cut chips 19 through the duct, a means for detecting the number of times by which the level of a change in output voltage exceeds a given threshold value, and a means for monitoring the above number of times in the unit machining operation and the level of a variation in the number of times between the unit machining operations to perform the detection of a deterioration in the drill or monitoring of the state of machining and the determination of whether or not the machined state is good.