The invention provides an image forming apparatus. The image forming apparatus includes a gradation correcting portion, an image forming device, a toner image fixing device, a fixing device mounting portion, a detector, and an executing portion configured to execute a calibration process for generating a gradation correction condition on the basis of a result of detection of a predetermined tonerimage by the detector. The predetermined toner image is a toner image which is formed, on the basis of predetermined data, on the recording material by the image forming device and which is fixed by the fixing device mounted in the mounting portion, and the predetermined toner image forms a plurality of image regions different in density. The executing portion permits execution of the calibrationprocess when the fixing device is the first fixing device, and prohibits the execution of the calibration process when the fixing device is the second fixing device.