An image forming apparatus makes use of a photosensitive sheet having a surface coated with microcapsules encapsulating a light-curable agent and a colorless dye and an image transfer sheet having one surface coated with a developing agent having an chromogenic effect on the encapsulated colorless dye. These sheets are superposed one on top of the other and pressed together by a compression device to selectively rupture the microcapsules on the photosensitive sheet, forming a visible image on the image transfer sheet which is thereafter heated by a heating device. Either the speed at which the image transfer sheet is passed through the compression device or the temperature at which the image transfer sheet is heated by the heating device is controlled according to a characteristic of the image transfer sheet such as its thickness, electrostatic capacity and light transmissivity.