PURPOSE: To enhance the rate of seisure of foreign matters whether they are of magnetic or non-magnetic substance and achieve a high quality by opening and shutting its contact so that an impact acts on in the axial direction of the reed switch at the time of reversals from the forward motion to the return motion and vice versa.

CONSTITUTION: When current is fed alternately to No.1 coil 1 and No.2 coil 2, a reed switch 5 is attracted to and collides with the core 3 of No.1 coil 1 and the core 4 of No.2 coil 2, and these motions are made repetitively. Because the coil 1, 2 are fed with current two times in the form of short pulse, the contact is once shut by the magnetic attraction force when the reed switch 5 runs against the core 3 or 4, then opened and again shut. With this reciprocative motions of the reed switch 5, foreign matters existing therein will move with the inertia force and get more chance of hopping in between the members of the contact. Then the contact is shut, and a contact touching resistance test is executed to sense a switch 5 as unacceptable which includs hopped-in foreign matters between the members of the contact. According to this system, the rate of foreign matter seisure is enhanced, and a high quality achieved.