Image forming apparatus including main body casing, fixing device attachable thereto, and spring configured to press boss of fixing device in attached state to main body casing

An image forming apparatus comprising:

• a main body casing;
• and
• a fixing device comprising a heating rotary body and a pressure rotary body, the fixing device being attachable to the main body casing from one side toward an other side in a first direction,
• wherein the main body casing comprises a first recessed portion recessed toward one side in a second direction crossing the first direction, and
• wherein the fixing device further comprises a first boss extending in a third direction crossing both the first direction and the second direction, the first boss being configured to be inserted in the first recessed portion in a state where the fixing device is attached to the main body casing,
• the image forming apparatus further comprising:
• a spring configured to press, in the state where the fixing device is attached to the main body casing, the first boss inserted in the first recessed portion toward both the one side in the first direction and the one side in the second direction.