The present invention provides a sheet feeder, which can reliably feed a sheet without requiring the extra operation of a regulating member, and an image forming apparatus.The sheet feeder comprises an intermediate plate 4 provided in a cassette body 2 so as to rotate in up and down directions around a rotation fulcrum portion 4a. The cassette body 2 has a freely movable rear end regulating member 5. The rear end regulating member 5 has a holding portion 5a which prevents the rotation fulcrum portion 4a of the intermediate plate 4 from being detached from the cassette body 2. In the transportation, the rear end regulating member 5 is set to a position where the holding portion 5a prevents the rotation fulcrum portion 4a of the intermediate plate 4 from being detached from the cassette body 2 and the intermediate plate 4 can rotate.