An image forming apparatus has an image forming apparatus main body with a sheet inlet. The main body is arranged to form an image on a sheet inserted into the sheet inlet. A roll paper cutting device contains roll paper and includes a cutting arrangement for cutting the roll paper and discharging cut sheets. The cutting device is attachable to the main body of the apparatus, and is selectively positionable to a feed position where its outlet is in register with the sheet inlet, or a standby position wherein the outlet thereof is out of register with the sheet inlet. A guide arrangement is provided on the main body for guiding the cutting device for movement in the vertical direction between the feed position and the standby position.