to the printing plate 2 wrapped around the plate cylinder 8 and is arranged so as to move along a guide portion 15 in the axial direction of the plate cylinder 8 the laser block moving unit 13 for moving this laser block 14 is bridged between the bearing portions 21r and 21l and includes a moving member 24 which is engaged with a lead screw 23 rotated by the laser block moving motor 34 so as to move a laser rod attaching base 50 of the laser block 14 is secured to the moving member 24 the assembled condition of the laser block 14 will be described with reference to fig6 to 8 fig6 is a perspective view illustrating the entirety of the laser block 14 in its assembled state fig7 is a partial cross sectional plan view of the assembled state of the laser block 14 and fig8 is an exploded perspective view of the laser block 14 as shown in fig6 to 8 a stepping motor attaching plate 51 is secured to a laser head mounting base 50 formed of a plate of substantially t letter configuration by screws and the stepping motor 46 is secured to this mounting plate 51 as shown in fig8 a first gear 52 is engaged into and secured to the rotary shaft of the stepping motor 46 a laser holder supporting box 53 is secured to the laser head mounting base 50 and the optical system of the semiconductor laser 1 or the like is assembled within this supporting box 53 the semiconductor laser 1 is secured to a semiconductor laser support 54 and is supplied with an electrical signal from a through hole 55 bored through the central portion of the semiconductor laser support 54 through a.