According to one embodiment, the image forming apparatus includes, an endless device having a plurality of suction holes, and a negative pressure chamber which communicates with the suction holes, a rotation mechanism which rotates the endless device, a suction mechanism which discharges air in the negative pressure chamber, an opening and closing mechanism which has a switching blade which opens and closes the suction holes, a driving mechanism which moves the switching blade to a first position and a second position, a recording head unit, a supply mechanism which supplies the recording medium to the endless device, and a controller. If the switching blade moves to the first position, the suction holes are shut. If the switching blade moves to the second position, the suction holes communicate with the negative pressure chamber. The controller drives the opening and closing mechanism according to the size of the recording medium.