To constitute a compact, light-weight, and inexpensive rotary joint capable of operating satisfactorily despite of the large number of electric signals.

This rotary joint is constituted by arranging electric power line carrier communication units on a tool side and a robot side of the rotary joint, respectively, and superimposing control signals on an electric power line of a slip ring for electric power in electric power line carrier communication to transmit and receive the control signals together with electric power. To explain concretely, this rotary joint is provided with a rotation side body rotating in the interlocking relationship with turn of a wrist of a robot, a fixed side body locked to prevent its turn for a robot arm, the slip ring for electric power arranged coaxially with a rotary shaft of the rotation side body, a power line carrier communication unit provided on a tool side rotating in the interlocking relationship with the rotation side body, and a power line carrier communication unit provided between a controller for tool and the rotary joint to connect with the electric power line carrier communication units by converting control signals of the controller for the tool and the tool.