PURPOSE: To enable to detect the control signal surely without being effected by noise, by detecting the synchronism between the specified control signal reproduced and the gated pulse based on this control signal to pick up the control signal.

CONSTITUTION: When the wave shape circuit 8 generates the pulse train according to the reproduced control signal in which a given frequency repeats the continuity and pause for a given time, the monostable multivibrator 10 is triggered with the leading of the first pulse to produce the pulse having specified long width. Further, the gated pulse having a half pulse width of the control signal is formed in synchronizing with the pulse with the control signal via the 1st and 2nd gated oscillators 12, 13 of the delay circuit 11 to perform clock control for the D type FF14, one bit binary FF15 fed with the control pulse. Thus, the AND gate 25 is open with the set pulse output only at the synchronism between the control pulse and the gated pulse by the RS type FF18 via the NOR gate 16, and the control signal detection output is output from the monostable multivibrator 26 to prevent malfunction.