Image forming apparatus

An image forming apparatus comprising:

• an image forming section configured to form an image on a recording medium with a first surface and a second surface;
• a fixing section configured to fix toner to the recording medium;
• a detector configured to detect a pair of marks formed on the second surface;
• and
• a controller configured to control the image forming section, the fixing section, and the detector, wherein
• the pair of marks is formed with ink that becomes transparent at a specific temperature or higher,
• the controller:
• calculates a calculated distance indicating a distance between the pair of marks based on a detection result of the detector after the fixing section has fixed the toner to the first surface;
• and
• calculates a shrinkage of the recording medium based on the calculated distance and directs the image forming section to form an image on the second surface according to the shrinkage, and
• the fixing section fixes the toner to the first surface at a first fixing temperature which is lower than the specific temperature, and fixes the toner to the second surface at a second fixing temperature which is higher than the specific temperature.