A controller drives a floating unit and a conveyor to perform a sheet feed operation, during the sheet feed operation, acquires an amount of received light at a detector during floating of sheets floated by the floating unit each time each sheet is conveyed by the conveyor, and perform a following control of lifting a stacking tray upon the acquired amount of received light being less than a threshold value. The controller, after start of the sheet feed operation, samples amounts of received light at the detector during floating of the sheets floated by the floating unit, performs a threshold value determination process of determining the threshold value by using the sampled amounts of received light, and starts the following control upon determining the threshold value.