A worm wheel comprising: a disk-shaped core made of metal; and a substantially annular rim portion made of synthetic resin and covering an outer circumferential portion of the core ; wherein a gear is formed on an outer circumferential portion of the rim portion , wherein the rim portion is integrally formed with the core by synthetic resin injection molding, wherein the core 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 is formed on a surface in a radially outer region of the first annular recess , wherein the other axial end surface of the core comprises end surface portions between which, in a radial direction, the second annular recess is disposed, and wherein each of the end surface portions is a flat surface, and wherein the flat surfaces forming the respective end surface portions are arranged on a same plane (F), wherein the rim portion comprises a first inner circumferential portion extending from an axial end surface of the rim portion 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 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 made of metal; and a substantially annular rim portion made of synthetic resin and covering an outer circumferential portion of the core ; wherein a gear is formed on an outer circumferential portion of the rim portion , wherein the rim portion is integrally formed with the core by synthetic resin injection molding, wherein the core 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 is formed on a surface in a radially outer region of the first annular recess , wherein the other axial end surface of the core comprises end surface portions between which, in a radial direction, the second annular recess is disposed, and wherein each of the end surface portions is a flat surface, and wherein the flat surfaces forming the respective end surface portions are arranged on a same plane (F), wherein the rim portion comprises a first inner circumferential portion extending from an axial end surface of the rim portion 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 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 . <EOS>