An image reader is provided, which includes a reference position determining unit configured to, in a state where a bright area and a dark area are formed on a reflection surface when a light projecting unit projects light toward a part of the reflection surface, receive the light reflected from the reflection surface with a light receiving portion of a reading unit while restricting a light emitting portion of the reading unit from emitting light, detect a position of the bright area and a position of the dark area in a main scanning direction, and determine a reference position in the main scanning direction based on the detected positions of the bright area and the dark area.