RECLINING DEVICE

PROBLEM TO BE SOLVED: To provide a reclining device that is operable by light operating force and has almost no variation in operating force regarding a reclining device which includes: an externally toothed gear that has external teeth formed on its outer peripheral surface and is provided at one of a member on a sheet cushion side and a member on a seat back side; and an internally toothed gear that is engraved with internal teeth, engaged with the external teeth of the externally toothed gear, has a larger number of teeth than that of the externally toothed gear, and that is provided at the other of the member on the seat cushion side and the member on the seat back side, and in which the rotary shaft of one of the externally toothed gear and the internally toothed gear revolves around the rotary shaft of the other of the gears.SOLUTION: The reclining device is configured such that a surface of an internal tooth 32b which is engaged with an external tooth 31b, is formed into a planar surface, and a surface of the external tooth 31b which is engaged with the internal tooth 32b, is formed into a convex surface projecting in the planar surface direction.