A centrifugal fluid machine (1, 2) including an impeller mounted to a rotation shaft; a housing for housing the impeller, an air intake duct structure being configured to direct a fluid (f) to a rotational center of the impeller housed in the housing via an intake duct portion of the housing protruding in an axial direction of the rotation shaft, the fluid (f) flowing in a substantially orthogonal direction to the axial direction of the rotation shaft, the centrifugal fluid machine (1, 2) not including a variable mechanism configured to swirl a fluid introduced into the impeller, the air intake duct structure comprising: an inflow part extending in the substantially orthogonal direction to the axial direction of the rotation shaft; and a transition part connecting the inflow part and the intake duct portion of the housing, characterized in that the air intake duct structure has a virtual plane orthogonal to the axial direction of the rotation shaft and passes through a flow path cross-section of the inflow part, where an intersection of the virtual plane and an axial direction line of the rotation shaft is positioned within the transition part, wherein, in a front view where the rotational center of the impeller is seen from its front, the air intake duct structure has a curved portion curved in a direction opposite to a rotational direction (r) of the impeller from the inflow part toward the transition part, wherein the transition part has a section from one end of the transition part to another end of the transition part, wherein the section has a shape bulging toward both of the outer and inner sides of the curved portion in the side view and a shape in the front view bulging toward an inner side of the curved portion such that the flow path cross-section between the one end and the other end is expanded. a housing for housing the impeller, an air intake duct structure being configured to direct a fluid (f) to a rotational center of the impeller housed in the housing via an intake duct portion of the housing protruding in an axial direction of the rotation shaft, the fluid (f) flowing in a substantially orthogonal direction to the axial direction of the rotation shaft, the centrifugal fluid machine (1, 2) not including a variable mechanism configured to swirl a fluid introduced into the impeller, the air intake duct structure comprising: an inflow part extending in the substantially orthogonal direction to the axial direction of the rotation shaft; and a transition part connecting the inflow part and the intake duct portion of the housing, characterized in that the air intake duct structure has a virtual plane orthogonal to the axial direction of the rotation shaft and passes through a flow path cross-section of the inflow part, where an intersection of the virtual plane and an axial direction line of the rotation shaft is positioned within the transition part, wherein, in a front view where the rotational center of the impeller is seen from its front, the air intake duct structure has a curved portion curved in a direction opposite to a rotational direction (r) of the impeller from the inflow part toward the transition part, an inflow part extending in the substantially orthogonal direction to the axial direction of the rotation shaft; and a transition part connecting the inflow part and the intake duct portion of the housing, characterized in that the air intake duct structure has a virtual plane orthogonal to the axial direction of the rotation shaft and passes through a flow path cross-section of the inflow part, where an intersection of the virtual plane and an axial direction line of the rotation shaft is positioned within the transition part, wherein, in a front view where the rotational center of the impeller is seen from its front, the air intake duct structure has a curved portion curved in a direction opposite to a rotational direction (r) of the impeller from the inflow part toward the transition part, wherein the transition part has a section from one end of the transition part to another end of the transition part, wherein the section has a shape bulging toward both of the outer and inner sides of the curved portion in the side view and a shape in the front view bulging toward an inner side of the curved portion such that the flow path cross-section between the one end and the other end is expanded.