To prevent a paper jamming at a discharged paper stacker part and further facilitate transferring printing papers in an opposite direction without generating a rattle of printing papers at the stacker part.

A gap reference part 21 for referring to a gap value, and a roller gap adjustment part 20 are set. At a printing start time, a gap between rollers 17 is made maximum to guide the printing paper 3. During printing, the printing paper 3 is sent to a stacker 2 by driving the rollers in a state while the gap between rollers 17 is made an optimum value to a thickness of the paper. Generation of the jamming is prevented and the rattle is prevented as well. Moreover, the printing paper can be smoothly transferred in the opposite direction by rotating both a tractor 11 and the rollers 17 in the opposite direction.