PURPOSE: To realize a short-length motor through reduction of unbalance of rotor by adjusting (increasing or decreasing) an applicable-balance or a detachable-balance, using an area which is naturally provided as a non-duty space, to a part of an armature core in the eccentric side and/or commutator side existing in such a direction where unbalance is generated.

CONSTITUTION: Weight is increased or decreased for taking the balance at the area unused as only a space around the shaft 2 and armature core of a motor. For instance, a part of the shaft is cut away for reducing the weight at the weight reducing portion 2a of the shaft 2. Moreover, an applied-balance material 3c consisting of a resin material is coated or a part of the weight reducing area 3d is cut away at the armature core 3a in the eccentric side and the armature core 3b in the commutator side. That is, an applicable-balance or a detachable-balance is provided to the shaft 2 and armature core to take the balance of the rotor as a whole. Thereby, a total length of the motor can be reduced and amount of resin for balance to be used can be reduced, resulting in cost reduction.