To prevent generation of white streaks without using a special head and form high-quality images by arranging a plurality of image form elements via a predetermined distance in a horizontal scanning direction and setting an image form head so that an arrangement direction of the image form elements tilts to a vertical scanning direction.

A light source 36 for fixing is set to the side of a transfer roller 32 of a thermal head 28 at a position spaced by a predetermined distance from a guide plate 38 to be opposite to the guide plate 38. The thermal head 28 has a plurality of rectangular heating elements R1-Rn arranged at predetermined intervals, preferably at equal intervals in a horizontal scanning direction of the thermal head 28. The heating elements adjacent to a platen roller 30 are connected to a power source via respective drivers. The thermal head 28 is set so that an arrangement direction of the heating elements R1-Rn tilts to a vertical scanning direction. In this case, an angle of not smaller than tan-1 (D/L) is preferred wherein D is the interval of the heating elements and L is a length of a part of the heating element in contact with the recording sheet.