In a scan apparatus, a sheet feeder having a sheet-stopping function includes a rotating shaft, a sheet-input roller, a pick-up mechanism and a sheet-stopping mechanism. The pick-up mechanism, including a bracket mounted on the rotating shaft and a pick-up roller mounted on the bracket, picks up a sheet from a paper tray. The sheet-stopping mechanism, driven independent of movement of the bracket by the rotating shaft, switches between a sheet-stopping state and a sheet-non-stopping state. The rotating shaft rotates in a first direction to enable the sheet-stopping mechanism to enter the sheet-non-stopping state and rotates in a second direction to enable the sheet-stopping mechanism to enter the sheet-stopping state, in which a passage to the sheet-input roller is blocked up.