PURPOSE: To enable the switching employment of high-density printing and high- speed printing by sliding a plurality of lines of wire pin guides which are provided slidably at the end of a wire impact type printer head.

CONSTITUTION: In a serial printer of wire impact dot type, a number of lines (three lines in the figure) of pin guides 5a1W5a3 each having a number of wire pin guide holes 5b are provided at the end of a printer head 5, and these guides are made slidable relatively. When high-density printing such as word processing is performed, the pin guides 5a1W5a3 are slided to increase the apparent density of pins in the vertical direction. When high-speed printing such as data processing is performed, the pin guides 5a1W5a3 are made to coincide in the horizontal direction and are operated alternately. It is suitable to employ a crank shaft 23 with crank arms 23a and 23b for sliding the pin guides 5a1W5a3.