To realize the water passage shape of a flat discharge bent pipe capable of restricting the peeling due to the flow and having excellent pressure restoring efficiency.

This flat discharge bent pipe changes the flow mainly flowing upward in the pump shaft direction into the horizontal direction at a part over a guide vane outlet (downstream) of a vertical shaft to lead the flow to a discharge flow passage arranged in the downstream and having a rectangular cross section. The inlet cross section is formed into an elliptic or a long circular shape for satisfying the relation B1x<B1y where B1x is an inlet width on the cross section including the center line of the discharge bent pipe and B1y is an inlet width in the direction at a right angle against the described inlet width B1x.