In an image reading apparatus, a white reference member for obtaining a reference value used in shading correction in the reading mechanism and an elastic member for cleaning a surface of the transparent member are provided such that respective positions of the white reference member and the elastic member with respect to the transparent member are variable. A controller controls the positions of these members with respect to the transparent member to alternately achieve movement of the white reference member to a position where the white reference member faces the transparent member and movement of the elastic member to a position where the elastic member faces the transparent member. The controller calculates the above reference value using a plurality of detection values read by the reading mechanism through the above positional control.