A fixing device fixing an image on a recording medium includes a fixing belt rotatable around a first rotation axis, a pressuring member, a heat source body and a cover member. The pressuring member forms a nip part pressuring and making the recording medium pass through with the fixing belt. The heat source body is arranged inside the fixing belt and heats the fixing belt by emitting radiant heat. The cover member is arranged between the fixing belt and the heat source body and covers the heat source body. The nip part has a passing area where the recording medium passes through and a non-passing area outside the passing area in an axial direction. The cover member covers a part of the heat source body corresponding to the non-passing area and includes through holes formed so as to adjust surface temperature of the heat source body.