In a first mode, an original is read with a first and a second carriages stopped. In a second mode, the original is read with the first and the second carriages moving in a sub-scanning direction with a distance between the original and an optical reading element kept constant. A control unit causes, if a predetermined condition is satisfied after reading the original in the first mode, the first and the second carriages to standby at a reading position of the first mode while keeping the light source turned on, and if a next read request is issued within a predetermined time, causes the first and the second carriages to move to a next reading operation.