A rotary machine includes: a shaft that rotates; a disc that has a substantially cylindrical hub fitted into the shaft and is provided so as to widen outward in a radial direction from a front end to a rear end of the substantially cylindrical hub; and an impeller having a plurality of blades provided on a surface of the disc. The substantially cylindrical hub has a tight fit section having an internal radius that is smaller than a radius of the shaft, and a loose fit section having an internal radius that is greater than the internal radius of the tight fit section. The loose fit section is provided on a front end side of the substantially cylindrical hub with respect to the tight fit section.