A rotary machine comprising: a nozzle configured to introduce a fluid from an outer circumferential side to an inner circumferential side in a radial direction; a volute having a substantially annular space in communication with the nozzle at the outer circumferential side; a guide section having a flow path in communication with the volute at the inner circumferential side of the volute, at which a plurality of vanes are installed in a circumferential direction, and configured to guide the fluid introduced from the volute; an accommodating chamber connected to the guide section in an axial direction and into which the fluid guided by the guide section is introduced; and an impeller accommodated in the accommodating chamber; wherein the volute comprises: an annular opening section in communication with the guide section at the inner circumferential side of the volute; a first inner wall surface extends from the opening section in the axial direction toward the impeller; and a second inner wall surface extends along the axial direction toward an opposite side of the impeller, wherein the width dimension of the volute in the axial direction is increased at both sides of the opening section to be larger than that of the opening section, characterised in that the plurality of vanes include: inner circumferential vanes vertically installed at the inner circumferential side of the volute; first outer circumferential vanes vertically installed at the outer circumferential side than the inner circumferential vanes and angled toward the nozzle; and second outer circumferential vanes vertically installed at intermediate positions of the inner circumferential vanes in the circumferential direction. a nozzle configured to introduce a fluid from an outer circumferential side to an inner circumferential side in a radial direction; a volute having a substantially annular space in communication with the nozzle at the outer circumferential side; a guide section having a flow path in communication with the volute at the inner circumferential side of the volute, at which a plurality of vanes are installed in a circumferential direction, and configured to guide the fluid introduced from the volute; an accommodating chamber connected to the guide section in an axial direction and into which the fluid guided by the guide section is introduced; and an impeller accommodated in the accommodating chamber; wherein the volute comprises: an annular opening section in communication with the guide section at the inner circumferential side of the volute; a first inner wall surface extends from the opening section in the axial direction toward the impeller; and a second inner wall surface extends along the axial direction toward an opposite side of the impeller, wherein an annular opening section in communication with the guide section at the inner circumferential side of the volute; a first inner wall surface extends from the opening section in the axial direction toward the impeller; and a second inner wall surface extends along the axial direction toward an opposite side of the impeller, wherein the width dimension of the volute in the axial direction is increased at both sides of the opening section to be larger than that of the opening section, characterised in that the plurality of vanes include: inner circumferential vanes vertically installed at the inner circumferential side of the volute; first outer circumferential vanes vertically installed at the outer circumferential side than the inner circumferential vanes and angled toward the nozzle; and second outer circumferential vanes vertically installed at intermediate positions of the inner circumferential vanes in the circumferential direction. inner circumferential vanes vertically installed at the inner circumferential side of the volute; first outer circumferential vanes vertically installed at the outer circumferential side than the inner circumferential vanes and angled toward the nozzle; and second outer circumferential vanes vertically installed at intermediate positions of the inner circumferential vanes in the circumferential direction.