An image reading apparatus includes: a reading unit outputting an output value based on reflection light from a sheet or a reference member; a white reference value generating unit generating a group of white reference values based on the output value under one of the plurality of reading conditions while the light source unit is turned on; a white reference value storing unit; a white reference value converting unit converting the group of white reference values into a group of white reference values of a different reading condition based on a correlation between the reading condition and the different reading condition; a sheet reading control unit controlling the reading unit to read the sheet while turning the light source unit on with the luminosity and lighting time stored in the white reference value storing unit; and a shading correcting unit performing a shading correction for the output value.