A bend pipe for supplying a fluid to a fluid machine or discharging the fluid from the fluid machine, the bend pipe comprising: an inlet pipe portion having a linear shape; a bend pipe portion connected to a downstream end of the inlet pipe portion and configured to change a flow direction of the fluid; and an outlet pipe portion having a linear shape connected to a downstream end of the bend pipe portion, wherein, provided that: a line including a pipe axial center line of the inlet pipe portion and an extension line thereof is defined as a line L; a line including a pipe axial line of the outlet pipe portion and an extension line thereof is defined as a line M; and a direction parallel to an intersection line formed by a plane orthogonal to the line M and a plane orthogonal to the line M is defined as a direction I, when, as seen from the direction I, a side of the line M on which the inlet pipe portion exists is defined as a front side and a side of the line M on which the inlet pipe portion does not exist is defined as a back side, a side surface on an outer side with respect to a bend direction of the bend pipe portion includes an outer inclined surface on the back side of the line M, the outer inclined surface being inclined so that a distance from the line M decreases toward a downstream side, wherein a pipe axial center line of the bend pipe portion has a back-side eccentric portion offset from the line M toward the back side, and the bend pipe portion includes, at least in a partial section, a cross section on which a gravity center is positioned on an inner side, with respect to the bend direction, of a center of a flow passage width in a direction orthogonal to the direction I, and, in the cross-section of at least a partial section of the bend pipe portion, the flow passage cross-sectional area (A2out) on the outer side, with respect to the bend direction, of the center of the flow-passage width (Wb) is smaller than the flow-passage cross-sectional area (A2in) on the inner side, with respect to the bend direction, of the center, characterized in that, at least in a partial section of the bend pipe portion, a vertex position at which a flow passage width of each cross section of the bend pipe portion is at a maximum is shifted about a pipe axial center line of the bend pipe portion toward a downstream side. an inlet pipe portion having a linear shape; a bend pipe portion connected to a downstream end of the inlet pipe portion and configured to change a flow direction of the fluid; and an outlet pipe portion having a linear shape connected to a downstream end of the bend pipe portion, wherein, provided that: a line including a pipe axial center line of the inlet pipe portion and an extension line thereof is defined as a line L; a line including a pipe axial line of the outlet pipe portion and an extension line thereof is defined as a line M; and a direction parallel to an intersection line formed by a plane orthogonal to the line M and a plane orthogonal to the line M is defined as a direction I, when, as seen from the direction I, a side of the line M on which the inlet pipe portion exists is defined as a front side and a side of the line M on which the inlet pipe portion does not exist is defined as a back side, a side surface on an outer side with respect to a bend direction of the bend pipe portion includes an outer inclined surface on the back side of the line M, the outer inclined surface being inclined so that a distance from the line M decreases toward a downstream side, wherein a pipe axial center line of the bend pipe portion has a back-side eccentric portion offset from the line M toward the back side, and the bend pipe portion includes, at least in a partial section, a cross section on which a gravity center is positioned on an inner side, with respect to the bend direction, of a center of a flow passage width in a direction orthogonal to the direction I, and, in the cross-section of at least a partial section of the bend pipe portion, the flow passage cross-sectional area (A2out) on the outer side, with respect to the bend direction, of the center of the flow-passage width (Wb) is smaller than the flow-passage cross-sectional area (A2in) on the inner side, with respect to the bend direction, of the center, characterized in that, at least in a partial section of the bend pipe portion, a vertex position at which a flow passage width of each cross section of the bend pipe portion is at a maximum is shifted about a pipe axial center line of the bend pipe portion toward a downstream side.