To efficiently and accurately determine an existence of a tool breakage.

In this device determining a breakage of a tool 5 by a needle 3 attached on a rotary shaft 2 of a motor 1 controlled by a controller 4, the motor 1 is forwardly and reversely rotated for detecting breakage of two tools 5 with one controller 4, and a rotation range of the motor 1 is regulated for preventing erroneous determination caused by contact of the needle 3 to an interfering object.