PURPOSE: To make an optical read invariably with the same sensitivity even when the start period of the read is not fixed by providing a charge detection part which detects a charge transferred from a CCD shift register and a gate means which takes out all charges stored in a photosensor.

CONSTITUTION: A signal 13 which is delayed a specific time Ts' behind a read start signal 10 is generated firstly. The read start signal 10 is applied to a leak gate terminal 9 to discharge carriers stored in the photosensor. A leak gate is closed at the fall of the read start signal 10 and integrating operation is started. The signal 13 is applied to a transfer gate terminal 7 a specific time T later to open the gate and carriers stored in the photosensor are transferred to the CCD shift register 1. The gate is closed at the fall of the signal 13 and then carriers are transferred to a carrier detection part 4 with a shift clock to obtain a video output at a terminal 6. When the time (t) when the leak gate is open is constant, the integration time T is Ts'-t. In this case, Ts' is constant, so the integration time T is constant without reference to Ts.