PURPOSE: To restrict an unlock operation of a spare tire carrier relating to a car body so that the operation can not be performed outside a car room, so as to place the operation under supervision particularly of a driver.

CONSTITUTION: A carrier lock mechanism is provided with a lock control lever 15e integrally turned with a disengaging lever 13 of a door lock device and an engaging protrusion provided in a carrier to rush into a car room inside through an insertion port of a rear door, to provide in the lock control lever 15e a circular arc-shaped slot 15e1 with a turn support point of the lock control lever serving as the center and a circular hole 15e2 larger than width of this slot in one end thereof, and the circular hole 15e2 is inserted to an engaging protrusion 25c. A head part 25c2, stopped to the circular arc-shaped slot 15e1 to regulate extraction, is formed to set a position relation of the lock control lever 15e to the engaging protrusion so that the circular hole 15e2 at inoperative time of the lock control lever 15e is opposed to the head part 25c of the engaging protrusion.