PURPOSE: To enable to adjust the mutual position of two cartridges of a swat type printer having two ink jet cartridges along the scan axis of a carriage.

CONSTITUTION: By this invention, the positioning between printhead cartridges C1, C2 along the media scan axis is carried out by adjusting the position of nozzle line in one side of printhead cartridges C1, C2 relative to the position of nozzle line in the other printhead cartridges C1, C2. These cartridges are supported by a carriage 51 of the printer and operated against the carriage 51 by a rotatable cam 111 supported by the carriage 51 provided with a cam lever 117. This cam 111 is rotated by the motion of the carriage 51 giving effects on an actuator arm 121. This actuator arm 121 is selectively positioned in accordance with the motion of carriage 51 inside and outside of the passage run across by the cam lever 117.