To provide a sheet processing device which can be comfortably used while reducing noise in contact regardless of the state of a sheet.

The sheet processing device 1 for receiving and aligning sheets one by one includes: a stacker 13 on the upper surface of which a sheet is placed; a regulating portion 13a provided at one end of the stacker 13 on which an end of the sheet abuts; a paddle member 11 having a plurality of blades 11a, and disposed above the stacker 13 to carry the sheet toward the regulating portion 13a by rotation; a paddle holding member 12 having a lower surface which is a downward convex not protruded beyond a trajectory circle drawn by tips of the blades 11a by the rotation of the paddle member 11 as viewed in the axial direction of a rotating shaft of the paddle member 11, and holding the rotating shaft of the paddle member 11; and a bias member which biases the paddle holding member 12 so that the lower surface approximates the upper surface of the stacker 13.