A label printer has a transfer portion of a toner image, a fixing portion, an unwinder that feeds a roll paper, a rewinder that takes up the roll paper, a conveyance mechanism 50 placed on the downstream side of the transfer portion in the conveying direction and on the upstream side of the fixing portion, and slack detection sensors 61, 62 that detect a slack degree of a medium between the transfer portion and the fixing portion. The conveyance mechanism 50 has a conveyance belt 51 to be rotated while mounting the medium on an upper surface facing the upper side, and an intake mechanism 52 for tightly fitting the medium to the upper surface of the conveyance mechanism 50. When selecting a mode to convey the roll paper, a paper feed unit controller controls passing speed at which the medium passes through a pass-through portion provided in the fixing portion in accordance with output signals from the slack detection sensors 61, 62.