An image reading apparatus including a shading correction mechanism that can be formed by fewer component parts than conventional ones, and is increased in the degree of freedom of design, thereby enabling reduction of the size and weight thereof. A contact glass guides an original to an image reading position. A glass holding member holds the glass. A line image sensor reads an image on the original conveyed to the image reading location, through the contact glass. A reference member is disposed at a location different from the image reading location on the contact glass. A moving mechanism relatively moves the line image sensor and the reference member so that the line image sensor can alternatively read the original conveyed to the image reading location and the reference member. A drive section externally drives the moving mechanism to move the line image sensor and/or the reference member.