The present invention addresses the problem of preventing a wire harness from detaching from a second arm, which is pivotally supported by a first arm, when the wire harness is fixed only at a harness fixing part at a rotating end of the second arm. In order to solve this problem, an arm power supply device (1) (1') is employed, the arm power supply device (1) (1') having a structure comprising a first arm (3) (3') that is rotatably supported by a base member (2), and a second arm (8) that is rotatably supported by the rotating end of the first arm. The second arm has a harness insertion groove (59) and a harness fixing part (58) at the rotating end, and the first arm has, at the rotating end, a flange part (60) (62) that covers the rotating base side of the harness insertion groove and prevents the harness from detaching. Either the flange part (60) is formed so as to protrude in the longitudinal direction of the first arm (3), or the flange part (62) is formed as a single continuous part extending in the longitudinal direction and the width direction of the first arm (3').