To provide a paper feeder provided with a rear end regulating plate with a simple composition needing no resetting even when sizes of recording mediums are changed.

A paper feeding tray 20 is provided with a lifting plate 22 supported rotatably around a shaft 21, and it is composed so it can approach a paper feeding roller 26 and so that a paper feeding roller 26 side tip of the lifting plate 22 is constantly energized upward by a spring. A side regulating plate 24 regulating a width direction position of a recording medium and the rear end regulating plate 25 regulating a conveyance direction rear end of the recording medium are fixedly arranged on the lifting plate 22. Since a plurality of step parts 25a, 25b, 25c, 25d, 25e or the like corresponding to the sizes of recording mediums are provided on the rear end regulating plate and a conveyance direction rear end position of at least a recording medium positioned in a lowest layer on the paper feeding tray is regulated, deviation is suppressed even when a position of the recording medium is deviated in the direction opposite to a conveyance direction following paper feeding action and the recording medium can be fed stably.