An image reading device includes a light source configured to irradiate a subject; a reading unit configured to detect reflected light generated by a subject reflecting light emitted from the light source, to perform reading; and a control unit configured to perform turn-on control on the light source. The control unit is configured to perform the turn-on control to change a turn-on condition such that the light source is turned on during a period when at least a detection region including an image pattern on the subject passes through a reading position of a reading unit, based on position information of the image pattern of the subject in a first operation mode for reading the subject, and perform the turn-on control to make the turn-on condition of the light source constant regardless of the image pattern of the subject in a second operation mode for reading the subject.