An image forming apparatus includes a sheet feeder, a sheet conveyor, an image former, a fixer, a colorimeter and a processor. The fixer fixes an image formed on a sheet by the image former. The colorimeter is provided on a down-stream side than the fixer in a sheet conveying direction and reads the image. The processor calibrates the colorimeter based on the image read by the colorimeter. When an image for calibration which is formed in advance on a color sample housed in the sheet feeder is made to be read by the colorimeter, the processor controls at least one of the sheet conveyor, the image former and the fixer according to a condition for controlling deterioration of the color sample which is different from a condition of when carrying out an image forming.