A motor case 21 is positioned to a gear case 31 in the diametrical direction by diametrically-positioning projection portions 72c of a brush holder 70 by causing the motor case 21 and the gear case 31 to face each other, and an axially-positioning projection portions 72e of the brush holder 70 are pressed from the axial direction of an armature shaft 24 by a pressing flange portion 21i, so that the brush holder 70 is positioned to the gear case 31 in the axial direction. Therefore, the size and weight of the rear wiper motor 10 can be reduced by avoiding enlargement of the coupling portion of the motor case 21 and the gear case 31, and since it is unnecessary to interpose the brush holder 70 in the coupling portion between the motor case 21 and the gear case 31, a sufficient seal performance can be obtained.