PURPOSE: To satisfactorily eliminate the energy dispersing signals in both scrambling systems by switching the clamp time constant of a dispersal eliminating circuit in accordance with the scrambling system of the received signal.

CONSTITUTION: When the scrambling system of the received signal is identical with a line rotation system, this fact is discriminated by a system deciding/voice descramble circuit 2. Thus a changeover switch SW is connected to a terminal (a). Then the clamp time constant of a dispersal eliminating circuit 3 is applied to the line rotation system so that a signal producing no line tilt is outputted. The scramble of this signal is released by a line rotation descramble circuit 4. meanwhile if the scrambling system is identical with a line permutation system, the circuit 2 discriminates this fact and the switch SW is connected to a terminal (B). Then a signal producing no field tilt is outputted and the scramble of the signal is released by a line permutation descramble circuit 5.