The DC motor has a field pole (3) having a main magnetic pole (4) of given axial length (Lm) and an auxiliary magnetic pole (5) and an armature core (6) of shorter axial length (Lc) than the main magnetic pole, rotating relative to the inner peripheral surface of the main magnetic pole. The edges of the main magnetic pole at either end of the given axial length are formed to ensure that the length (Ln) of the straight part between the pole edges is greater the axial length of the armature core, but less than 1.15 times this length.
