To configure an air passage capable of absorbing rotations between arms without a rubber hose.

An air supplying annular groove 23, and an exhausting annular groove 24 are formed on a shaft 13 for transmitting rotations of a motor provided on a wrist portion to a flange. On a sleeve 17 fitted with the shaft 13, relay passages 19, 20 communicating with both annular grooves 23, 24 are formed, and an air supplying conduit 15 and an exhausting conduit 16 provided on the wrist portion are connected to those relay passages 19, 20. Relay passages 25, 26 communicating with both annular grooves 23, 24 are formed on the shaft 13, and an air supplying connecting pipe 29 and an exhausting connecting pipe 30 provided on the flange 8 are connected to those relay passages 25, 26. Concerning O-ring grooves 36, 38, the curvature radius of a corner portion A outside is made to be large, thereby easing stress concentration, and filling rings 42, 43 are fitted on the corner portion A side.