a waiting tray is provided at some midpoint of a conveying path , and a sheet is caused to be in a waiting state when a post - process is required . before performing the post - process , a processing tray receives the sheet conveyed from the waiting tray and the sheet conveyed from a conveying path without passing through the waiting tray . the waiting tray is formed by waiting tray parts which are arranged at a predetermined interval , and a strike - down mechanism is operated . therefore , a bundle of paper loaded on the waiting tray is caused to fall down on the process tray .