To simplify a unit and to obtain the unit wherein selection of surface and back surface is easily performed in relation to a printing unit wherein one face monocolor printing can be performed by changing selectively the surface and the back surface of a continuous paper.

In a surface/back surface changing type one face monocolor printing unit 10, there exist printing plate cylinders 2a and 2b between which a blanket cylinder 3 is placed and ink roller groups 11a and 11b consisting of ink distributing rollers 12a and 12b, ink reciprocating rollers 13a and 13b and form rollers 14a and 14b are respectively provided and they are brought into contact with ink ductor 7 and an ink and a damping water are respectively fed to the printing plate cylinders 2a and 25 respectively from an ink fountain 6 and dampening apparatus 8a and 8b. Rotations of the printing plate cylinders 2a and 2b and the blanket cylinder 3 are changed normally and reversely by means of a changing mechanism and either one of the ink distributing rollers 12a and 12b is changed by means of a mounting and removing mechanism so as to bring it into contact with the ink ductor 7 to print selectively either one face of a continuous paper between the cylinders 3 and 2a or 3 and 2b.