To provide a sheet processing device capable of delaying the interruption of the work by the determination of the full condition by allowing a plurality of stack trays 18a, 18b to be in a full condition.

When the full condition of a stack tray 18a on the upper stage is determined, the delivery destination is changed to a stack tray on the lower stage and the loading is continued without any other change. When the full condition of a stack tray 18b on the lower stage is determined, the full condition is firstly processed to prohibit the further delivery of the sheets. Since the stack tray 18a on the upper rank is preferentially filled, the lowering position of the stack tray 18b can be kept higher than that when the stack tray 18b on the lower rank is filled, and the interference with a saddle tray 106 arranged below a stack tray 18c or the book-bound sheet bundle stacked on the saddle tray 106 can be avoided.