A headrest side connector unit mounted on a headrest of a vehicle includes a stay as a holder and a connector. The connector includes a projection 430 to be received in a projection insertion hole formed on the stay. A tip part of the second connector at a side to be connected to the mating connector is disposed further outside of the stay than an end of the stay near a seat. An outer surface of the tip part is arranged on the same plane as an outer surface of the end of the stay.
