POWER SUPPLY DEVICE

A power supply device configured to supply power to a seat S that is movable relative to a floor F of a vehicle includes a power receiving unit that includes a power receiving coil and configured to move along with the seat S, a power transmitting unit that includes a power transmitting coil disposed opposing the power receiving coil and configured to supply power to the power receiving coil in a contactless manner and a power transmitting extension portion extending from the power transmitting coil , the power transmitting unit being configured to move along with the seat S and the power receiving unit , and a slack absorption portion that includes a winding portion configured to wind and feed the power transmitting extension portion by rotating in coordination with the movement of the seat S.