1. A video signal regulating apparatus including a lamp for illuminating an original document, optoelectric scanning means for scanning the document and producing electrical video signals corresponding to an optical pattern thereof and amplifier means for amplifying the video signals, characterized by comprising: sensor means comprising a single sensor which is disposed so as to simultaneously receive reflected light from the document and light from the lamp and being connected to the amplifier means, the amplifier means being constructed such that an amplification factor thereof varies in accordance with an output of the sensor means to regulate a level of the video signals to a constant valve.