PURPOSE: To reliably detect the attaching condition of metal powder by generating an output signal in response to the attaching condition of metal powder, generating a comparison signal when the output signal is lower than the reference voltage, and turning a warning light on in response to the comparison signal.

CONSTITUTION: When metal powder attaches to the detection gap of a chip detector 1, a resistor RC is changed depending on the sticking condition. The voltage changed according to the change of the resistor RC is obtained at a point B and inputted to a comparator 2. On the other hand, the predetermined reference voltage is obtained at a point A and inputted to the comparator 2. The comparartor 2 compares the input voltage with the reference voltage at the point A and generates a comparison signal when the input voltage is lower than the reference voltage. This comparison signal is fed to a warning light driver 4 via a resistor R8 and a capacitor C1 and causes a warning light 3 to be lighted invariably with predetermined and sufficient intensity. Accordingly, the attaching condition of metal power can be reliability detected by the lighting of the warning light.