In a pressure developing device, employed in an image recording unit, including a pair of pressure developing rollers for pressurizing a material on which a visible image is to be developed through elastic springs, provided are backup rollers arranged to be brought into contact with each of the pair of pressure developing rollers. Thus, a pressure force generated between the pair of pressure developing rollers are uniformly applied to the material along a direction which the pair of pressure developing rollers are extended. Further, a pressure force, i.e., a length of each of the elastic springs is arranged to be adjusted from the outside of the pressure developing device with a simple operation by means of a screw and so forth.