An image scanning device has a light source for emitting a beam, a CCD circuit board having a CCD sensor, an optical unit for guiding the emitted beam from the light source to the CCD sensor, a CCD sensor driving circuit connected with the CCD circuit board with a signal cable, a clock generating circuit for generating a clock to be transferred to the CCD sensor, a reset pulse generating circuit for generating a reset pulse for resetting an output buffer of the CCD sensor, a clamp circuit for clamping an output of the CCD sensor, and an analog-to-digital converter for converting an analog signal into a digital signal. The clock generating circuit is disposed on the CCD circuit board.