Planetary gear having non-circular gears

A planetary gear device, comprising a non-rotatable casing, an input shaft driven for rotation by a drive source, means rotatably supporting said input shaft inside and on said non-rotatable casing, a carrier fixed on said input shaft and extending radially from said input shaft, an output shaft rotatably supported in said non-rotatable casing, a plurality of planetary shafts connected at one of the respective ends thereof to said carrier and equispaced from each other on a circle concentric with the rotational axis of said input shaft, a plurality of planetary gear units each integrally comprising a main driving gear and a driven gear and each being rotatably supported on the respective planetary shaft of said plurality of planetary shafts, an output gear fixed on said output shaft and meshing with said driven gears, and a fixed gear fixed to said non-rotatable casing and meshing with said main driving gears, wherein at least either the combination of said main driving gears and said fixed gear or the combination of said driven gears and said output gear forms pairs of non-circular gears whose pitch curves are configured in rotational symmetries, wherein said plurality of planetary shafts corresponds in number to said rotational symmetries, and wherein said planetary shafts are arranged symmetrically with respect to said input shaft.