Provided is a robot pivot shaft structure that includes a revolving drum rotatably supported at an upper portion of a base and that has a hollow portion, a drive motor rotating the revolving drum, and a speed reduction mechanism reducing the rotational speed of the drive motor. The speed reduction mechanism has a small gear fixed to a shaft of the drive motor, a large gear meshed with the small gear, an input hypoid gear fixed to the large gear, and an output hypoid gear meshed with the input hypoid gear. The output hypoid gear is fixed to the revolving drum and is disposed in the base. The input hypoid gear and the large gear are rotatably supported at the base. The drive motor is fixed to the base and disposed below the revolving drum, the position being horizontally shifted from vertically below the hollow portion.