PURPOSE: To enable monochromatic printing and bicolor printing to be performed on one surface and the other of paper respectively and besides the surface where bicolor printing is performed to be easily changed by using an offset printer having a pair of right/left rubber barrels provided between a pair of right/left lower plate barrels arranged at an appropriate interval and an upper plate barrel installed above between said lower plate barrels and also said rubber barrels set in movable fashion.

CONSTITUTION: Paper 6 is inserted between rubber barrels 4, 5 which are open in a neutral state, and then is printed in monocolor by plate barrels 1, 2 on the both sides when moved in an arrow direction with the rubber barrels 4, 5 set in the first position (b). In addition, if the rubber barrel 4 is set to the second position (c) and the rubber barrel 5 to the third position (d), the left surface of the paper 6 is printed in two colors by the plate barrels 1, 3, while the right surface is printed in monocolor by the plate barrel 2. Furthermore, if the rubber barrel 4 is set to the third position and the rubber barrel 5 to the second position, the left surface of the paper 6 is printed in two colors by the plate barrels 2, 3, while the left surface of the paper 6 is printed in monocolor by the plate barrel 1.