A sheet post-process apparatus includes a waiting tray and a processing tray. The waiting tray is provided in the middle of a conveying path and makes standby sheets in the case where a post-process is required. The processing tray has a function which causes the sheets made standby on the waiting sheet to be dropped by self-weight. With this function, the processing tray receives the sheets moved to be dropped and the sheets conveyed from the conveying path without intervening the waiting tray, before carrying out the post-process. Sheet bundles formed on the processing tray are stacked on a storage tray by a sheet conveying mechanism after they have been post-processed.