PURPOSE: To enable the detection of metal without any contact thereto and prevent an effect due to noises by forming a detecting matrix of a receiving line and transmitting line combined to cross each other and disposed on the opposite surface or a base plate and interrupting transmission according to a noise signal of a receiving circuit or changing over the frequency to one not affected by noises.
CONSTITUTION: A plurality of transmitting lines 22 and receiving lines 26 are constituted to meander in parallel and coupled electromagnetically to each other to cross orthogonally to each other and form a planer detecting matrix 20 for constituting a metal sensor along the board face. When a magnetic field is generated by the transmission through the transmitting line 22, an electromotive force is generated in the receiving line 26. When a pinball approaches then a detecting unit 20a, the electromotive force is varied and a position of the ball is grasped. A transmission interrupting means 57 interrupts the transmission by a transmitting circuit 40 according to a noise signal from a noise detecting means 55. On the basis of the measuring result of a noise level measuring means 36, a frequency change-over means 38 changes over the frequency to one of two kinds of preset frequencies which is not affected by detected noises.
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KAWASHIMA KAZUNARI
HANDA SHIGERU
