Image reading apparatus and copier

An image reading apparatus includes a line sensor for reading an image of an original, a scanning optical system that has a light source and scans the original, a reference reflection member provided in such a position as to reflect a light emitted from the light source, a buffer memory for storing data of the image, an intermittent reading part interrupting and restarting scanning performed by the scanning optical system based on a residual storage capacity of the buffer memory, and a light amount variation correction part correcting a variation in an amount of light of the light source during an interruption of the scanning based on an amount of reflected light from the reference reflection member.