When an image reader is in a stand-by state in which the image reader can read
an original, supply of a clock signal from a clock generation circuit to a line
sensor is halted. Hence, supply of a clock signal does not need power. As a result
of supply of the clock signal to the line sensor being halted, there can be reduced
generation of a dark current due to the head developing in the line sensor and
generation of Electromagnetic Interference. Consequently, the noise in read image
data is reduced, thereby improving the picture quality of a read image. In the
stand-by state, supply of only a clock signal to the line sensor is halted. Hence,
the time required for warming up the line sensor is nominal. Upon receipt of a
reading instruction, the image reader can immediately start reading an original,
thus improving operability of the image reader.
