A sheet ejection device includes a sheet receiving tray provided with a sheet stack plane, a detector for detecting ejected sheets at a reference position, and a controller. Both side end of the sheet stack plane is made higher than a center thereof when viewed along a sheet ejection direction. The reference position functions as a reference for a height level of a center of an uppermost surface of stacked sheets on the sheet stack plane. During a sheet ejection operation, the controller moves the tray downward by a preset height level every ejection of a preset number of sheets until the detector detects sheets, and then newly starts to move the tray downward by the preset height level every ejection of the preset number of sheets from a time when the detector detects sheets. According to the device, sheets can be prevented from being stacked on the tray erroneously.