A sheet discharging tray device includes: a discharging section from which a sheet is discharged; a discharging tray on which the sheet discharged from the discharging section is stacked sequentially; a tray drive section which drives the discharging tray in a tray shift direction that is perpendicular to a sheet discharging direction from the discharging section with reference to a sheet surface; a controller which conducts a tray shift operation that shifts a position of the discharging tray under a condition of the number of sheets stacked on the discharging tray, and a sheet detection section which detects an alignment deviation in the tray shift direction. The controller changes an operation status of the discharging tray when a tray shift operation is conducted and changes a discharging operation of a sheet to the discharging tray, based on a detected result of the sheet detection section.