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 L 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 characterized in that the bend pipe portion has, at least in a partial section, a flattened shape in which a flow passage width in a direction J orthogonal to the direction I is smaller than a flow passage width in the direction I. 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 L 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 characterized in that the bend pipe portion has, at least in a partial section, a flattened shape in which a flow passage width in a direction J orthogonal to the direction I is smaller than a flow passage width in the direction I. <EOS>