A sensor magnet assembly has a cylindrical shape extending in an axial direction and includes a fixing member fixed to a one side end of a shaft in the axial direction and a sensor magnet fixed to an outer circumferential surface of the fixing member. The fixing member includes a first groove recessed inward from the outer circumferential surface in a radial direction and has an annular shape extending in a circumferential direction and first recesses recessed inward from the outer circumferential surface in the radial direction and spaced apart along the circumferential direction. The first recesses are disposed at positions different from the first groove in the axial direction. The first groove and the first recesses are disposed in a portion of the outer circumferential surface of the fixing member, to which the sensor magnet is fixed.