PURPOSE: To make it possible to automatize easily a polarity test by a method wherein such a magnetization as to have a magnetic pole in the direction of the polarity of a diode is performed on a magnetic material applied on an electronic component or built in the component.

CONSTITUTION: In a constant-voltage diode or the like, a polarity display 2 of the diode is printed on an electronic component. Moreover, a magnetic paint 3 is applied on the surface of the component and such a magnetization as to have a magnetic pole in the direction to show the polarity of the diode is performed on this paint 3. That is, the magnetization is performed in such a way that the side of an anode of the diode and the side of a cathode of the diode are respectively set into an N pole and an S pole. Thereby, at the time of mounting of the diode on a circuit board, the discrimination of the polarity can be performed utilizing a magnet and a verification of the polarity can be performed utilizing the magnet in a test subsequent to the mounting.