Abstract: A serial printer has a type drum rotating about a rotation axis perpendicular to the direction of the line of a paper and a carriage for carrying said type drum in the direction of the line. The carriage has a type drum comprising a base member and type belts disposed round said base member at different levels, and a hammer rotatably supported on said carriage. One end of said hammer is led into the interior of said drum and disposed opposed to the type part of said type drum. Another end of said hammer is in the exterior and disposed to contact with a cam. When said another end comes into contact with said cam, said hammer is rotated by said cam whereby a type on said type belts is pushed out against the paper by said one end of said hammer to effect printing.