To selectively print on both front and back surfaces of rotary printing paper without changing a rotating direction of a printing cylinder of a printing unit.

A front and back surfaces printer comprises the printing unit A having the printing cylinder rotating in a predetermined direction and being selectively rotatable in a feeding direction of the rotary printing paper 11 by the printing cylinder to an upstream side or a downstream side of the feeding direction of the paper, and guide rollers 12a, 12b, 12c, 13a and 13b for inverting the front surface back side the paper fed from the upstream side of the feeding direction of the paper to the upstream side of the feeding direction of the printing cylinder of the unit rotated so as to direct the downstream side of the feeding direction of the cylinder to the upstream side of the feeding direction of the paper at a periphery of the unit and supplying the paper.