The invention relates to a transfer mechanism for transferring an image on a photosensitive drum (4) onto an image forming member (2), and the transfer mechanism is provided with a mechanism (28-2, 40 to 47) for changing the curvature of the print medium (2) bent by the transfer guides (10) in order to make the transfer performance of print mediums having different stiffness uniform, in addition to an approach/retraction mechanism (28-1, 50 to 56) of the transfer guides (10). Since the amount of bite of the print medium to the image forming member can be changed by changing the curvature according to the type of a print medium, a uniform transfer press force can be maintained without the occurrence of transfer displacement, thereby print quality can be improved in various types of print mediums.