Patent ID: 7409185

Claim:
A sheet post-process apparatus, the apparatus comprising: a waiting tray which temporarily retains a transported sheet, and releases the retention to drop the sheet; a processing tray which bundles sheets dropped from the waiting tray to carry out predetermined processing, and ejects the sheets, wherein the waiting tray makes a next sheet standby, so as not to be transported to the processing tray, until the predetermined processing of a preceding sheet on the processing tray has been completed; a storage tray which holds the bundle of sheets processed and ejected on the processing tray, wherein the waiting tray comprises: left and right lower face support members which support left and right lower faces in a sheet transport direction during retention and release the support of the left and right lower faces during release of the retention; an extensible tray coupled to the left and right lower face support members, the extensible tray being projectively provided in a proximal end direction of the transported sheet, and remaining in a projected position after sheets have been dropped from the waiting tray; drive means for projecting the extensible tray in a transport distal end direction of the sheet; and control means for controlling the drive means, and the control means controls the drive means to project the extensible tray in the transport proximal end direction of the sheet when it is sensed that a size of a sheet transported to the waiting tray exceeds a size set on the waiting tray, based on information concerning a size of the sheet transported to the waiting tray; and sensor means for sensing height of sheets held on the waiting tray, wherein the control means controls the drive means to adjust a projection length of the extensible tray, based on the height of sheets sensed by the sensor means.