To provide an image reader that can accurately detect the position of a carriage even when the step angle of a motor is changed.

This image reader reads the image of an original by exposing and scanning the original by moving carriages 5 and 8 mounted with optical systems by means of a motor 21 which is rotated by a prescribed step angle by a clock pulse, and, at the same time, detects the reading position by counting the number of clock pulses by means of a counter. The motor 21 is constituted of a motor that can change the step angle rotated by one clock pulse. This image reader is provided with a motor clock generating circuit 23 which multiplies a number of clocks in accordance with the switching ratio at the time of switching the step angle of the motor 21.