An electric turbo compressor is an air compressor to be used in a fuel cell system, and includes a housing comprised of a compression casing, a motor casing, and a canceller casing, and the housing houses therein an impeller, a rotary shaft, a thrust canceller (a load cancellation section), and a motor unit. The rotary shaft is supported by a thrust air bearing in its thrust direction, and is axially supported by a radial air bearing in its rotating direction. A thrust load is generated at the rotary shaft when the number of rotations of the impeller increases. The pressure of the compressed air acts to the pressure chamber from the compressed air lead-out section of the compression casing via the compressed air passage, and this pressure acts on the canceller flange of the canceller shaft so as to generate a load towards the rear of the rotary shaft. Therefore, the thrust load is cancelled out.