To provide a dot-line printer low in cost and high in reliability without generating the deterioration or shortage of a lubricant.

The dot-line printer comprises: a hammer bank 1 mounted with a plurality of print hammers 10; a paper feeding mechanism for conveying printing paper 3; a platen 5 supporting a printing force of the print hammer 10; and a platen opening and closing mechanism which positions and displaces the platen 5 by striking an eccentric cam 12a eccentric with respect to a rotating shaft on the platen 5 or a member holding it for moving to and from in the right-angled direction with respect to the printing paper 3. Furthermore, the eccentric cam 12a is constituted of a porous sintered body mainly composed of metal powder with oil impregnation.