Reduction gear for vehicle seat

A reduction gear for a vehicle seat is provided with a worm (7) connected to an end of a drive shaft (31a) and formed integrally with and on a common axis with a threaded portion (71) of the worm (7), a worm wheel (8) formed on a common axis with an output shaft (82b) and meshed with the worm (7), and a casing (6) rotatably supporting the worm (7) and the worm wheel (8) meshed with each other. The casing (6) has a worm fitting sleeve (62) for accommodating the worm (7), and the worm fitting sleeve (62) incorporates a leaf spring (9) which pushes the worm (7) in its axial direction with an extreme end of the worm (7) held in contact with the leaf spring (9).