A power supply device for a sliding door (12) comprising an extra-length absorbing unit (14), a door side fixing unit (16) fixed to a sliding door, a flexible tube (18) extending from said extra-length absorbing unit (14) to said door side fixing unit (16), and a wire harness (20) wired from a vehicle body (10) through said extra-length absorbing unit (14), said flexible tube (18) and said door side fixing unit (16) to the sliding door (12),
wherein said extra-length absorbing unit (14) includes a case (30) having a gate (28) for said flexible tube, a rotating drum (32) for winding said flexible tube in the case, and a torsion spring (34) for providing a turning force with said rotating drum in a winding direction of said flexible tube.