A DC motor comprising: a tubular housing having a plurality of flat lateral surfaces and flat or curved corners connecting adjacent lateral surfaces, the lateral surfaces forming a polygonal cross section; a magnet provided along the inner circumference of the housing and having magnetic poles (60, 61, 62, 63) at the corners of the housing; a shaft configured to be inserted into the housing along the axial line of the housing; an armature secured to the shaft and provided to face the magnet; a commutator fitted to the shaft so as to be coaxial with the armature; a carbon brush having a columnar body and provided in the housing such that the longitudinal direction of the body being aligned with the radial direction of the commutator, the end surface of the brush being in sliding contact with the outer circumference of the commutator; a support provided in the housing and configured to support the carbon brush in a manner that the stroke of the brush in the radial direction of the commutator is allowed; and a biasing member provided in the housing and configured to bias the carbon brush toward the commutator, wherein the carbon brush is provided such that longitudinal direction of the brush is aligned with the diagonal line of the polygon, the housing comprises a metal case and a resin brush holder connected together, the magnet being secured to the metal case and the brush holder supporting the carbon brush, and the corner of the brush holder is provided with a tubular carbon holder configured to support the carbon brush such that the stroke of the brush in the radial direction of the commutator is allowed, and the carbon holder includes only two holders including a first carbon holder and a second carbon holder, an angle formed by a direction of stroke of a first carbon brush supported by the first carbon holder and a direction of stroke of a second carbon brush supported by the second carbon holder being 90°. a tubular housing having a plurality of flat lateral surfaces and flat or curved corners connecting adjacent lateral surfaces, the lateral surfaces forming a polygonal cross section; a magnet provided along the inner circumference of the housing and having magnetic poles (60, 61, 62, 63) at the corners of the housing; a shaft configured to be inserted into the housing along the axial line of the housing; an armature secured to the shaft and provided to face the magnet; a commutator fitted to the shaft so as to be coaxial with the armature; a carbon brush having a columnar body and provided in the housing such that the longitudinal direction of the body being aligned with the radial direction of the commutator, the end surface of the brush being in sliding contact with the outer circumference of the commutator; a support provided in the housing and configured to support the carbon brush in a manner that the stroke of the brush in the radial direction of the commutator is allowed; and a biasing member provided in the housing and configured to bias the carbon brush toward the commutator, wherein the carbon brush is provided such that longitudinal direction of the brush is aligned with the diagonal line of the polygon, the housing comprises a metal case and a resin brush holder connected together, the magnet being secured to the metal case and the brush holder supporting the carbon brush, and the corner of the brush holder is provided with a tubular carbon holder configured to support the carbon brush such that the stroke of the brush in the radial direction of the commutator is allowed, and the carbon holder includes only two holders including a first carbon holder and a second carbon holder, an angle formed by a direction of stroke of a first carbon brush supported by the first carbon holder and a direction of stroke of a second carbon brush supported by the second carbon holder being 90°.