In an apparatus for producing a printing image on a printing medium held by a cylinder (1) by a laser, the laser writing head (7) of which is positioned on a crossmember (3) so as to be displaceable parallel to the axis of the cylinder (1), a space-saving functionally reliable embodiment is attained by the fact that a protective switch (10) which detects the presence of a cylinder (1) is provided fixedly on the crossmember (3) and the crossmember (3) bears switching strips (5, 6) which expose a laser writing head displacement region (b) between them having the width of the printing image (8) and interact with a further protective switch (11) attached to the laser writing head (7) for switching off the laser when it is situated outside the laser writing head displacement region (b).