An image forming apparatus may includes: an apparatus body; a fixing device removably mounted to the apparatus body and including a first fixing member, a heat generation member which heats the first fixing member, a second fixing member forming a fixing nip between the first fixing member and the second fixing member, and a housing accommodating at least the heat generation member and the first fixing member and provided with a communication part communicating between inner and outer sides of the housing; a transfer member arranged upstream of the fixing device in a conveyance direction of a recording sheet, and to which developer is configured to be transferred; a sensor configured to detect the developer transferred to the transfer member; and a film arranged to cover the sensor between the communication part and the sensor.