To provide technology for shortening reading time in an image reader which operates a transportation section and a carriage by a common motor.

An image reader includes a switch gear and a control section. The switch gear is changed over to a carriage side position (FB side position) which couples a motor side transmission gear and a carriage side transmission gear for transmitting force to a carriage, and a transportation section side position (ADF side position) for coupling the motor side transmission gear and a transportation section side transmission gear for transmitting force to a transportation section transporting a document. The control section performs prediction processing (steps S31, S32) for predicting whether a carriage reading (FB reading) mode for moving the carriage which holds a reading section and reading the image is performed or not before a reading start instruction of the image is received by the reading section and a switching processing (step S34) for switching the switch gear to the carriage side position when the carriage reading mode is predicted to be performed.