A worm wheel (10A, 10B) comprising: a disk-shaped core (1A, 1B) made of metal; and a substantially annular rim portion (2A, 2B) made of synthetic resin and covering an outer circumferential portion of the core (1A, 1B); wherein a gear is formed on an outer circumferential portion of the rim portion (2A, 2B), wherein the rim portion (2A, 2B) is integrally formed with the core (1A, 1B) by synthetic resin injection molding, wherein the core (1A, 1B) comprises a center hole into which a shaft is capable of being fitted, an axial end surface formed with a first annular recess, and another axial end surface formed with a second annular recess, characterized in that a third annular recess (14, 14A) is formed on a surface in a radially outer region of the first annular recess, wherein the other axial end surface of the core (1A, 1B) comprises end surface portions (13a, 13b) between which, in a radial direction, the second annular recess is disposed, and wherein each of the end surface portions (13a, 13b) is a flat surface, and wherein the flat surfaces forming the respective end surface portions (13a, 13b) are arranged on a same plane, wherein the rim portion (2A, 2B) comprises a first inner circumferential portion extending from an axial end surface of the rim portion (2A, 2B) to a radially outer region of the first annular recess and fixed to a radially outer region of a bottom surface of the first annular recess, a second inner circumferential portion extending from another axial end surface of the rim portion (2A, 2B) to a radially outer region of the second annular recess and fixed to a radially outer region of a bottom surface of the second annular recess, and a protrusion engaged with the third annular recess wherein an outer circumferential wall surface of the second annular recess extends from a bottom surface of the second annular recess so as to be perpendicular to the bottom surface. a disk-shaped core (1A, 1B) made of metal; and a substantially annular rim portion (2A, 2B) made of synthetic resin and covering an outer circumferential portion of the core (1A, 1B); wherein a gear is formed on an outer circumferential portion of the rim portion (2A, 2B), wherein the rim portion (2A, 2B) is integrally formed with the core (1A, 1B) by synthetic resin injection molding, wherein the core (1A, 1B) comprises a center hole into which a shaft is capable of being fitted, an axial end surface formed with a first annular recess, and another axial end surface formed with a second annular recess, characterized in that a third annular recess (14, 14A) is formed on a surface in a radially outer region of the first annular recess, wherein the other axial end surface of the core (1A, 1B) comprises end surface portions (13a, 13b) between which, in a radial direction, the second annular recess is disposed, and wherein each of the end surface portions (13a, 13b) is a flat surface, and wherein the flat surfaces forming the respective end surface portions (13a, 13b) are arranged on a same plane, wherein the rim portion (2A, 2B) comprises a first inner circumferential portion extending from an axial end surface of the rim portion (2A, 2B) to a radially outer region of the first annular recess and fixed to a radially outer region of a bottom surface of the first annular recess, a second inner circumferential portion extending from another axial end surface of the rim portion (2A, 2B) to a radially outer region of the second annular recess and fixed to a radially outer region of a bottom surface of the second annular recess, and a protrusion engaged with the third annular recess wherein an outer circumferential wall surface of the second annular recess extends from a bottom surface of the second annular recess so as to be perpendicular to the bottom surface.