A thermal type image forming apparatus is provided for printing images on both sides of a medium, which are a first surface and a second surface of the medium. A thermal print head (TPH) is rotated about a platen roller to a first position facing the first surface of the medium and to a second position facing the second surface of the medium. The thermal type image forming apparatus includes a transfer unit for transferring the medium in a first direction to supply the medium to a space between the platen roller and the thermal print head and in a second direction substantially opposite to the first direction to perform printing. A control member controls motion of the platen roller in the second direction to align a printing nip formed by the platen roller and the TPH with a heating line of the thermal print head. The platen roller is elastically biased in a direction to contact the control member.