The invention discloses a motor and a play detection device of an output shaft thereof, which comprise a casing and a speed reducer, wherein a rotor is arranged in the casing, an output shaft of the rotor extends out of the casing, the speed reducer comprises a worm wheel, a casing body and a worm, the worm is arranged at the end part of the output shaft, the worm wheel is connected to the casing body in a rotating way, the casing is fixed on the casing body, the output shaft extends into the casing body, the worm and the worm wheel are matched, the end part of the output shaft is provided with a sleeve of which the outer surface is a spherical face, a positioning component is arranged in the casing body, a hole is arranged on the positioning component, the sleeve is connected to the hole in a rotating way, grooves communicated with the inner wall of the hole are arranged on the positioning component, and a clamping arm is formed between the grooves. When the deviation of the installation position of a body occurs, the installation of the body still can not be influenced even if a certain angular offset exists between the output shaft and the positioning component because the outer surface of the sleeve is the spherical face.