PURPOSE: To keep the clearance between a printing head and a recording paper at constant value by a method wherein a collision member, moving into fore- and-back directions together with the printing head with respect to the recording paper, is provided, and the collision member is removed after the head is fixed upon the collision thereof.

CONSTITUTION: The printing head is energized by an energizing means such as a tension spring 5 or the like so as to be retreated from the recording paper (printed medium) 27. The collision member 6 is moved toward the recording paper together with the printing head by a driving means consisting of a wire 19, pulleys 8, 14, 16 and a driving source pulling the wire 19 and when this collision member 6 is collided against the printing medium of the recording paper, the printing head is fixed at the position by a locking means such as a lock lever 11, a lock pin 18 and the like, thereafter, the collision member 6 is separated from the recording paper 27 by a retreating means such as a lock control lever 13 and the like.