A sheet stacking device includes a device main body, a sheet discharge unit, a sheet stacking portion and a sheet detector. The sheet discharge unit discharges sheets. The sheet stacking portion includes a sheet stacking surface on which the sheets are to be stacked. The opening is formed in the sheet stacking surface. The sheet detector includes a detection piece capable of projecting upwardly of the sheet stacking surface from the opening. The sheet detector detects a first state, a second state and a third state. The first state is a state where no sheet is placed on the sheet stacking surface. The second state is a state where a first number of the sheets discharged are placed on the sheet stacking surface. The third state is a state where a second number of the sheets larger than the first number are placed on the sheet stacking surface.