PURPOSE: To simplify the assembly of a thrust bearing and the adjustment of bearing load.

CONSTITUTION: In the case of the thrust bearing assembly regulating method of a motor with a worm decelerator, a thrust bearing furnishing hole 14 is openingly provided on the extension line of a rotary shaft 2 at a housing 4 made of resin. A thrust bearing metal 12 is inserted into this bearing furnishing hole 14, and goes on entering under pressure while supersonic wave energy is being energized. At the time of this entering under pressure, the rotary shaft 2 is rotatingly driven electrically, and at the same time this rotary drive electric current value is measured. When the measured electric current value reaches a set value, the operation of entering under pressure and the operation of supersonic wave energy energization with regard to the bearing metal 12 are stopped. As a result, the bearing metal 12 can be fixed at the housing 4 by means of a welding portion 15 formed by means of supersonic wave energy. Simultaneously, the bearing load of the bearing metal 12 can be adjusted automatically.