the pattern dependent on movements of the sheet and the pen p in x y directions a pen switching mechanism according to another embodiment of the invention will be described in detail with reference to fig6 8 a 8 c and 9 a 9 c a pen holder 52 with a ratchet shaft 67 connected therewith is rotatably supported between a rear wall 50a and a support base 56 the pen holder 52 has in its peripheral surface four angularly equidistant slots 52a for holding front portions of pens p and four angularly equidistant slots 52b for holding rear portions of the pens p the slots 52a 52b are axially aligned with one another a pen return leaf spring s on the pen holder 52 has four small diameter holes sa for insertion therein of the tip ends of the pens p which are normally biased resiliently by the spring s to move away from the platen 10 fig1 the pen holder 52 has a stopper flange 52c at a rear end thereof against which the rear ends of the pens p are held under the resiliency of the return spring s a slot 52d formed in and across the rear end of the pen holder 52 is shaped for splined engagement with the ratchet shaft 67 a pawl plate 57 has a pawl 57a formed on an upper end thereof and held in engagement with.