POWER SUPPLY DEVICE

The present invention is to prevent the entry or the like of foreign matters between a support member and a swingable rotary member when, for example, a sliding door is fully opened. A power supply device (1) includes: a rotary member (5') that holds a wire harness (48) inserted therethrough; and a support member (3') that swingably supports the rotary member and is fixed to a fixed structure body (53) or a sliding structure body (54), wherein the rotary member has an annular outer peripheral wall (15) and a harness lead-out portion (21), the support member has one sidewall (8') disposed along the outer peripheral wall, and the harness lead-out portion moves in a direction away from the sidewall when the sliding structure body is fully opened, the outer peripheral wall is widely exposed between the harness lead-out portion and the sidewall, and the outer peripheral wall and the sidewall are overlapped with each other in a plate thickness direction in a state where the outer peripheral wall is widely exposed and come close to or come in contact with each other, so that foreign matters are prevented from entering between the outer peripheral wall and the sidewall.