To provide a wheel adapter that enables a wheel having a different number of holes and PCDs to be mounted without cutting heads of hub bolts even on a vehicle having hub bolts fixed to a hub in advance.

This wheel adaptor has hub bolt passing holes 21a, 21b through which the hub bolts are made to pass, and a bolt attachment part where a wheel-fastening bolt is attached. A part of the bolt attachment part is formed of a recessed part 20 which is formed at the wheel side of the wheel adapter body, and an auxiliary member 3 to which a flat head bolt 5b with a hexagonal hole as the wheel fastening bolt is mounted and fixed in the recessed part 20. This recessed part 20 has screw holes 25 for fastening the auxiliary member 3 and the hub bolt passing hole 21b. The auxiliary member 3 has bolt passing holes 30 through which bolts 4 with a hexagonal hole fastened to the screw holes 25 of the recessed part 20 are made to, and a hub bolt containing hole 31 which is formed at a position facing the hub bolt passing hole 21b of the recessed part 20 with a diameter larger than that of the hub bolt.