To improve the S/N of picture signals by controlling the frequency band of analog picture signals to be inputted to an A/D converter.

Analog signals outputted from a video camera 1 are amplified in a preamplifier 2 and then led to an AGC circuit part 3, a peak value or average value of a signal voltage is detected in a signal voltage detection part 31 and a control voltage corresponding to the detected signal voltage is generated in an AGC control voltage generation part 32. The control voltage is fed back to the preamplifier 2 of a preceding stage to control the gain of the preamplifier 2 and is also inputted to a control terminal of a pre-filter 4 of a poststage to shift the cutoff frequency of the pre-filter to be lower than the cutoff frequency set under sufficient illumination. Signals passed through the pre-filter 4 are converted to digital signals in an A/D converter 5 and then, image compression for transmission is executed in the compression encoder 6.