A wiper motor comprising an electric motor and a motion conversion mechanism converting a rotary motion of the electric motor into a swinging motion and transmitting the swinging motion to an output shaft, comprising: a speed reduction mechanism comprising a worm rotated by the electric motor, and a worm wheel meshing with the worm, the speed reduction mechanism reducing the speed of rotation of the electric motor and transmitting the rotation to the motion conversion mechanism; a bottomed gear frame attached to the electric motor, and formed with a speed reduction mechanism chamber storing the speed reduction mechanism and a motion conversion mechanism chamber storing the motion conversion mechanism; a supporting face flush with an axial end face of the worm wheel rotatably contained in the speed reduction mechanism chamber is formed on a bottom wall of the motion conversion mechanism chamber; a gear cover closing an opening of the gear frame; a pinion gear fixed to a proximal end of the output shaft, slidably struck on the supporting face of the gear frame, and integrally rotating with the output shaft; a motion conversion member comprising a sector gear portion meshing with the pinion gear, rotatably connected to the worm wheel at a position deviating radially from an axial center of the worm wheel, and slidably struck on the supporting face of the gear frame and the axial end face of the worm wheel; and a retaining plate connecting a gear shaft provided at an axial center of the sector gear portion and the output shaft swingably to each other, characterized in that: the supporting face of the gear frame is formed over an entire area facing the pinion gear and the motion conversion member of the bottom wall of the motion conversion mechanism chamber, and the pinion gear and the motion conversion member slide over an entire area facing the supporting face of the gear frame. a speed reduction mechanism comprising a worm rotated by the electric motor, and a worm wheel meshing with the worm, the speed reduction mechanism reducing the speed of rotation of the electric motor and transmitting the rotation to the motion conversion mechanism; a bottomed gear frame attached to the electric motor, and formed with a speed reduction mechanism chamber storing the speed reduction mechanism and a motion conversion mechanism chamber storing the motion conversion mechanism; a supporting face flush with an axial end face of the worm wheel rotatably contained in the speed reduction mechanism chamber is formed on a bottom wall of the motion conversion mechanism chamber; a gear cover closing an opening of the gear frame; a pinion gear fixed to a proximal end of the output shaft, slidably struck on the supporting face of the gear frame, and integrally rotating with the output shaft; a motion conversion member comprising a sector gear portion meshing with the pinion gear, rotatably connected to the worm wheel at a position deviating radially from an axial center of the worm wheel, and slidably struck on the supporting face of the gear frame and the axial end face of the worm wheel; and a retaining plate connecting a gear shaft provided at an axial center of the sector gear portion and the output shaft swingably to each other, characterized in that: the supporting face of the gear frame is formed over an entire area facing the pinion gear and the motion conversion member of the bottom wall of the motion conversion mechanism chamber, and the pinion gear and the motion conversion member slide over an entire area facing the supporting face of the gear frame. the supporting face of the gear frame is formed over an entire area facing the pinion gear and the motion conversion member of the bottom wall of the motion conversion mechanism chamber, and the pinion gear and the motion conversion member slide over an entire area facing the supporting face of the gear frame.