To absorb dislocation of the axis of an input shaft and an outer race, without generating an abnormal sound, in a speed increaser of a supercharger.

This supercharger 10 has the speed increaser 20 comprising the outer race 27 rotated by the input shaft 11 and a plurality of intermediate rollers 31 to 33 arranged in an annular space between the outer race 27 and an output shaft 12, and is formed by connecting the input shaft 11 and the outer race 27 by a drive member 28, and slidably connects the input shaft 11 in the (x) axis direction to the drive member 28, and slidably connects the drive member 28 in the (y) axis direction orthogonal in the (x) axis direction to the outer race 27.