Abstract: Inaccurate duplication of the first and the secnd prints due to the inequality of the distance and arrangement therebetween occurs in a serial printer in which a carriage is moved parallel to a platen by a servo motor etc. The first printing in duplex printing is performed after sufficient time for damping of the oscillation of the carriage in this invention. The second printing is done after sufficient time for damping of the oscillation as well as before. The control may be performed by sensing the necessary carriage displacement. The duplex printing may be performed when the displacement is zero or a small value.