PURPOSE:To allow the fall of the pulse signals obtained with one moving body to coincide with the point of time when the moving object goes out of the detecting loop irrespective of the kinds of the moving object by changing the threshold value based on the change in the output signal proportional to effective inductances. CONSTITUTION:When a vehicle arrives at a detecting loop 1, the effective inductance of the loop 1 decreases and the frequency of the output signal of an oscillating circuit 2 changes. The output signal of a resonance circuit 3 is conducted to a phase discriminating circuit 4. The circuit 4 receives the output signal of the circuit 2 as well and produces the output signal of the voltage value proportional to the phase difference of both signals. The output signal of the circuit 4 is conducted to a peak holding circuit 5 and a comparator 6. In the circuit 5, the peak value of the output signal of the circuit 4 is detected. The threshold value of the comparator 6 is set at the value corresponding to this peak value.
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