A structure of a robot includes: a first member having a hollow portion in the vicinity of a horizontal axis; a second member rotatably supported on a side surface of the first member and having a hollow portion in the vicinity of the horizontal axis; a drive motor producing power for rotating the second member; and a speed reducer reducing the rotation speed of the drive motor and transmitting the rotation to the second member. The speed reducer includes: an output hypoid gear formed of a ring gear disposed coaxially with the horizontal axis and fixed to the first member; an input hypoid gear engaged with the output hypoid gear; and a transmission mechanism transmitting rotation from the drive motor to the input hypoid gear while reducing the speed. The drive motor, the input hypoid gear, and the transmission mechanism are supported in the second member in an accommodated state.