A commutator includes a cylindrical insulator and commutator pieces, which are formed on the outer circumferential surface of the insulator and arranged side by side in the circumferential direction of the insulator. The commutator pieces are each composed of a conductive plate material, and each includes a connection claw and an engagement claw. The connection claw extends outward in the radial direction of the insulator while being configured to electrically being connected to an armature coil. The engagement claw extends inward in the radial direction of the insulator and engages with the insulator. The commutator pieces each include a recess portion with an undercut formed in a surface facing inward in the radial direction of the insulator.