The present invention relates to an air supply system for a vehicle, which includes a curved diffuser passageway and a volute formed on upper portion of the diffuser passageway to sufficiently secure a length of the diffuser passageway, thereby enhancing a pressure conversion efficiency and reducing a size of the entire system, and which further includes a guide for guiding an air flow toward an input of an impeller, thereby minimizing a loss occurring when air passing through a motor housing flows to the inlet of the impeller, and reducing a weight of an outlet duct.