PURPOSE: To prevent clipping and to prevent reduction in the effective bit number by providing an attenuator controlling the attenuation rate in response to a detection output of a level detection circuit and a variable gain amplifier circuit controlling the amplification factor in response to the detection output to the title device.

CONSTITUTION: The attenuation rate of a picture signal inputted to an A/D converter circuit 4 is controlled by an attenuator 2 so that clipping of a signal to be inputted is prevented in response to the detection output of a level detection circuit 3 and the amplification factor for the picture signal outputted from a D/A converter circuit 6 is controlled by a variable gain amplifier circuit 7 so that the level of the picture signal is equal to the level of the input to the attenuator 2 in response to the detection output of the level detection circuit 3. Thus, the clipping of the signal inputted to the A/D converter circuit is prevented and the reduction in the effective bit number in a reference input level is avoided.