When a printing conveyance speed at a printing unit is changed, if a length of a printing paper sheet in the conveyance direction thereof is smaller than an inter-unit conveyance distance, which is set in advance, between the printing unit and a post-processing unit, only a printing suspending operation at the printing unit is performed, and a post-processing suspending operation at the post-processing unit is not performed. On the other hand, if the length of the printing paper sheet in the conveyance direction thereof is equal to or greater than the inter-unit conveyance distance, both the printing suspending operation at the printing unit and the post-processing suspending operation at the post-processing unit are performed. In this manner, the post-processing suspending operation is omitted depending on the length of the printing paper sheet in the conveyance direction thereof.