A spindle motor and a disk drive device are provided that have a high operation efficiency of the motor, that does not leak oil, and that has an improved stability by decreasing a runout component in the direction of the rotation axis. The spindle motor includes a rotor hub (20) composed of a disk-like flange (201) and a cylinder-shaped shaft (203); a ring-shaped rotating magnet (16) fastened on one main surface of the flange (201); an armature (14) facing the rotating magnet (16); a sleeve (80) rotatably supporting the shaft (203); and a chassis (15) fixing the armature (14) and the sleeve (80). The flange (201) and the shaft (203) are integrally formed with magnetic material; a protrusion is not provided between a mounting surface (204) for mounting the rotating magnet (16) thereon and a counter-face surface (205) facing the end surface of the sleeve; and the mounting surface (204) and the counter-face surface (205) are orthogonal to the direction of the central axis (A-A′) of the shaft (203), and in a level plane; or the mounting surface (204) is recessed stepwise from the counter-face surface (205) toward the disk mounting portion (202).