An air supply device of a vehicle is provided to prevent excessive vibration of a rotation shaft and the damage to peripheral parts of an impeller due to the contact of the impeller by an auxiliary bearing. An end plate(180) seals an opened lower end of an outlet duct(160) and is mounted with an auxiliary bearing(181) for keeping a uniform clearance with respect to a rotation shaft(141). The clearance between an inner diameter part(181a) of the auxiliary bearing and the rotation shaft is 0.3%~3% of the inner diameter of the auxiliary bearing.