PURPOSE: To increase the printing speed of a printer by arranging two printing hammers provided on a printing head in parallel each other with an interval corresponding to a specific multiple of the lateral pitch of a dot matrix.

CONSTITUTION: Plural lines of elongated protruded part 2 are formed, in parallel each other, on the outer circumference of a rotary drum 1 in the direction of its axis and a printing head 5 equipped with 2 pieces of print hammer 10, 10a to be electromagnetically driven which is fixed to a carriage 6 supported by 2 pieces of guide shaft 7 to be freely slidable are provided to oppose each other through a recording medium 3 and an ink ribbon 4 so that they can be moved in the direction of the axis of the drum 1. The hammers 10, 10a are caused to change their opposing positions in parallel each other with an interval corresponding to n multiple (n>1) of the lateral pitch Ph of a dot matrix against the protruded part 2 in its longitudinal direction and simultaneously they are caused to drive alternately with an interval cycle of the time the protruded part 2 requires to move the dot matrix vertically by its vertical pitch Pv.