A motor output shaft positioning device for motors with worm reduction gears for outputting the output of a motor output shaft via a worm reduction gear, comprising a gear case having a hollow part for housing a worm fitted to a motor output shaft and a worm wheel meshing with the worm and receiving an end of the motor output shaft; the hollow part receiving a bearing of the motor output shaft and a steel ball; a bearing holder having projections projecting towards the bottom of the hollow part, and a filler that is injected into the hollow part through a filling hole formed on the hollow part.