6 and the original sensor 27 via a bus 48 the rom 41 stores programs for executing various processes of the image scanning apparatus 1 the programs may include but not be limited to a maintenance main process a scanning main process and processes for subroutines of each main process the cpu 40 controls the respective units and components in accordance with programs read from the rom 41 the flash prom 43 is a nonvolatile memory which is readable and writable and stores various types of data such as data generated during a control process and data calculated in the maintenance main process the ram 42 temporarily stores data such as calculation results generated by the control process by the cpu 40 the device controller 44 is connected to the scanning device 24 in accordance with instructions from the cpu 40 the device controller 44 transmits to the light source 30 a signal for controlling on or off of the light source 30 and a signal for controlling a current value flowing through the light source 30 further as shown in fig3 the device controller 44 transmits to the light receiving unit 31 a serial in signal si for transferring electric signals of the plurality of photoelectric conversion elements 33 to the shift register and a clock signal clk for sequentially outputting the electric signals from the shift register when the scanning device 24 receives these control signals from the device controller 44 the scanning device 24 turns on the light.