An image forming apparatus includes a fixing unit and an apparatus main body. The fixing unit includes a first rotating member, a second rotating member and a fixing nip forming mechanism. The first rotating member is heated by a heating source. The second rotating member faces to the first rotating member. The fixing nip forming mechanism makes the second rotating member pressed to the first rotating member and forms a fixing nip between the first rotating member and second rotating member. To the apparatus main body, the fixing unit is attachably/detachably installed. The apparatus main body includes a nip pressure changing mechanism. The nip pressure changing mechanism presses the fixing nip forming mechanism and changes a pressure of the fixing nip.