To provide a seat lifter with improved convenience.

A base 31 is mounted on an inner block 23 constituting a ball screw engaged to a pole 22 inside a linear guide 20, and an arm 34 and a plate 35 for supporting an auxiliary seat are rotatably supported at a barrel part 33 of the base 31. A pin 56 to be inserted into a notch 51 of the plate 35 and a recess 52 of an attaching part 41 is mounted on a seesaw lever 55 supported by the plate 35. A lever 63 is rotatably supported at a holding part 62 of the base 31, and a guide 69 in which an inclining part 81 is formed is held between a first bearing 66 and second and third bearings 67 and 68 of a bearing bracket 65. The lever 63 and a projecting pin of the plate 35 are connected with a link 72 to rotate the arm 34 according to the tilting of the lever 63.