A worm wheel (4a, 4b, 4c, 4d) comprising: an inner wheel element (15a, 15b, 15c, 15d); and an outer wheel element (16a, 16b, 16c, 16d), wherein: the inner wheel element (15a, 15b, 15c, 15d) includes a first annular concave part (22, 22a) provided to be recessed in an axial direction in an axial one-side surface, a second annular concave part provided to be recessed in the axial direction in an axial other-side surface, and an outer circumferential surface thereof is formed to be a cylindrical surface part in which a diameter in the axial direction is not changed; and the outer wheel element (16a, 16b, 16c, 16d) is made of a synthetic resin, has a worm wheel tooth part in an outer circumferential surface, and embeds the inner wheel element characterized in that a first concave-convex part (23, 23a) is provided in an outer diameter side circumferential surface constituting an inner surface of the first annular concave part (22, 22a) in a circumferential direction, and a second concave-convex part is provided in an inner surface of the second annular concave part in a circumferential direction, the outer wheel element (16a, 16b, 16c, 16d) embeds the inner wheel element so as to cover a continuous range from a radial intermediate portion of a bottom surface constituting the inner surface of the first annular concave part (22, 22a), through an outer circumferential surface of the inner wheel element (15a, 15b, 15c, 15d), to an inner diameter side circumferential surface constituting at least the inner surface of the second annular concave part in a surface of the inner wheel element over an entire circumference, the synthetic resin partially enters into a concave part constituting the first concave-convex part (23, 23a) and a concave part constituting the second concave-convex part. an inner wheel element (15a, 15b, 15c, 15d); and an outer wheel element (16a, 16b, 16c, 16d), wherein: the inner wheel element (15a, 15b, 15c, 15d) includes a first annular concave part (22, 22a) provided to be recessed in an axial direction in an axial one-side surface, a second annular concave part provided to be recessed in the axial direction in an axial other-side surface, and an outer circumferential surface thereof is formed to be a cylindrical surface part in which a diameter in the axial direction is not changed; and the outer wheel element (16a, 16b, 16c, 16d) is made of a synthetic resin, has a worm wheel tooth part in an outer circumferential surface, and embeds the inner wheel element characterized in that a first concave-convex part (23, 23a) is provided in an outer diameter side circumferential surface constituting an inner surface of the first annular concave part (22, 22a) in a circumferential direction, and a second concave-convex part is provided in an inner surface of the second annular concave part in a circumferential direction, the outer wheel element (16a, 16b, 16c, 16d) embeds the inner wheel element so as to cover a continuous range from a radial intermediate portion of a bottom surface constituting the inner surface of the first annular concave part (22, 22a), through an outer circumferential surface of the inner wheel element (15a, 15b, 15c, 15d), to an inner diameter side circumferential surface constituting at least the inner surface of the second annular concave part in a surface of the inner wheel element over an entire circumference, the synthetic resin partially enters into a concave part constituting the first concave-convex part (23, 23a) and a concave part constituting the second concave-convex part. the inner wheel element (15a, 15b, 15c, 15d) includes a first annular concave part (22, 22a) provided to be recessed in an axial direction in an axial one-side surface, a second annular concave part provided to be recessed in the axial direction in an axial other-side surface, and an outer circumferential surface thereof is formed to be a cylindrical surface part in which a diameter in the axial direction is not changed; and the outer wheel element (16a, 16b, 16c, 16d) is made of a synthetic resin, has a worm wheel tooth part in an outer circumferential surface, and embeds the inner wheel element characterized in that a first concave-convex part (23, 23a) is provided in an outer diameter side circumferential surface constituting an inner surface of the first annular concave part (22, 22a) in a circumferential direction, and a second concave-convex part is provided in an inner surface of the second annular concave part in a circumferential direction, the outer wheel element (16a, 16b, 16c, 16d) embeds the inner wheel element so as to cover a continuous range from a radial intermediate portion of a bottom surface constituting the inner surface of the first annular concave part (22, 22a), through an outer circumferential surface of the inner wheel element (15a, 15b, 15c, 15d), to an inner diameter side circumferential surface constituting at least the inner surface of the second annular concave part in a surface of the inner wheel element over an entire circumference, the synthetic resin partially enters into a concave part constituting the first concave-convex part (23, 23a) and a concave part constituting the second concave-convex part.