To provide a rotary machine that makes it possible to prevent leakage of high-pressure gas from division surfaces without providing irregularity on a contact surface of each of an upper flange portion and a lower flange portion. The rotary machine according to the present invention includes: a casing 101; a rotor 2 that includes a rotatable rotary shaft 3 located inside the casing 101, and a plurality of stages of impellers 4 fixed to an outer periphery of the rotary shaft 3; a diaphragm group 5 including diaphragms 51 that are respectively provided in the plurality of stages of the impellers 4; gas flow paths provided respectively corresponding to the impellers 4 and through which process gas to be compressed flows; and a discharge volute 57 connected to the gas flow paths. The discharge volute 57 is provided to expand inward in an axis line direction Da of the casing 101.