To rapidly replace a conveying belt to be used for conveyance when the conveying belt is qualitatively deteriorated caused by sticking or paper dust or the like.

Conveying belts 21a-21e which serve for conveying printing paper, advancing into a paper conveyance path and the conveying belts 21a-21e to be sidetracked from the paper conveyance path, are selectively switched using a belt switching means 10. When the conveying belts 21a-21e are qualitatively deteriorated caused by the sticking of paper dust or the like, either of the conveying belts 21a-21e which is eligible for conveyance duty can be rapidly switched.