Provided is a power supply device capable of suppressing bulge of a wire harness toward a vehicle body when a slide door is half-opened. The power supply device is provided with a wire harness arranged between a vehicle body and a slide door, a portion of the wire harness on the vehicle body side extending in the closing direction of the slide door when the slide door is half-opened, and a door side coil spring (a biasing part) for biasing a portion of the wire harness on the slide door side in the biasing direction pressing against the slide door on the closing direction side of the slide door in order to suppress a curvature convex toward the inside of the vehicle body at the time of half-opening of the slide door.