[Problem] To provide a swing-type speed reducer that has a large crossing angle, and that can be further miniaturized compared to conventional speed reducers.
[Solution] Provided is a swing-type speed reducer 1 comprising: a main body 10; an input shaft 20 that is rotatably held in the main body 10; a precession body 30 that precesses; a swinging body 40 that engages with the precession body 30 and is swung by the precession; and an output shaft 50 that is rotated by the swing of the swinging body 40. In the present invention, a precession annular groove 34 for precession of the precession body 30 and a swinging annular groove 33 for swinging the swinging body 40 are provided on the surface of a spherical portion 31. Thereby, in comparison to a conventional case where the grooves are provided on the inner peripheral surface of a member, the region where the grooves can be machined is increased, and the device can be further miniaturized.