PURPOSE: To provide a semiconductor laser drive device allowing highly accurate light quantity control by minimizing an quantization error in analogue/digital conversion without using an expensive analogue/digital converter having a large number of bits.

CONSTITUTION: A target value memorized in a signal processing circuit 6 corresponding to a light quantity of a target outgoing light is converted into an analogue signal by a digital/analogue converter 11, signal voltage and the analogue signal converted by a current voltage converter 3 are inputted into a differential amplifier 4 as an input signal. Then, an output from the differential amplifier 4 is converted into a digital signal by an analogue/digital converter 5 and outputted to a signal processing circuit 6. This signal processing circuit 6 performs digital signal processing and a digital control signal for driving a semiconductor laser 1 is outputted to a digital/analogue converter 8.