A paper feeder comprising: a cassette capable of being loaded into and unloaded from an apparatus body in a predetermined direction, the cassette being provided internally with a sheet container in which sheets are to be contained; a sheet conveyance path which is extended from the sheet container and along which the sheet is to be conveyed in a sheet conveyance direction; a paper feed roller mounted to the cassette at an entrance of the sheet conveyance path and configured to convey the sheet in the sheet conveyance direction; and an opposed member disposed opposite to the paper feed roller and forming, together with the paper feed roller, a paper feed nip where the sheet enters;- characterized in that: the sheet conveyance direction extends along a direction of loading and unloading of the cassette; and the paper feeder further comprises a restricting member configured to, in a first state where the cassette is unloaded from the apparatus body, close off a portion of the sheet conveyance path upstream of the paper feed nip in the sheet conveyance direction to restrict the sheet in the sheet container from entering the paper feed nip and, in a second state where the cassette is loaded in the apparatus body and the paper feed roller is ready to convey the sheet, open the sheet conveyance path to allow the sheet enter the paper feed nip. a cassette capable of being loaded into and unloaded from an apparatus body in a predetermined direction, the cassette being provided internally with a sheet container in which sheets are to be contained; a sheet conveyance path which is extended from the sheet container and along which the sheet is to be conveyed in a sheet conveyance direction; a paper feed roller mounted to the cassette at an entrance of the sheet conveyance path and configured to convey the sheet in the sheet conveyance direction; and an opposed member disposed opposite to the paper feed roller and forming, together with the paper feed roller, a paper feed nip where the sheet enters;- characterized in that: the sheet conveyance direction extends along a direction of loading and unloading of the cassette; and the paper feeder further comprises a restricting member configured to, in a first state where the cassette is unloaded from the apparatus body, close off a portion of the sheet conveyance path upstream of the paper feed nip in the sheet conveyance direction to restrict the sheet in the sheet container from entering the paper feed nip and, in a second state where the cassette is loaded in the apparatus body and the paper feed roller is ready to convey the sheet, open the sheet conveyance path to allow the sheet enter the paper feed nip. the sheet conveyance direction extends along a direction of loading and unloading of the cassette; and the paper feeder further comprises a restricting member configured to, in a first state where the cassette is unloaded from the apparatus body, close off a portion of the sheet conveyance path upstream of the paper feed nip in the sheet conveyance direction to restrict the sheet in the sheet container from entering the paper feed nip and, in a second state where the cassette is loaded in the apparatus body and the paper feed roller is ready to convey the sheet, open the sheet conveyance path to allow the sheet enter the paper feed nip.