Described herein is a floating flap gate including a gate leaf having a buoyancy forming portion, the gate leaf being configured to be raised due to buoyancy effect (e.g., from water), a bottom fitting mounted to a proximal end portion of the gate leaf, the bottom fitting having a convex circular arc-shaped surface across a width direction of the gate leaf, a plate member having a concave circular arc-shaped surface to be mated with the convex circular arc-shaped surface of the bottom fitting when the gate leaf is in a lowered state, wherein the concave circular arc-shaped surface is in contact with the convex circular arc-shaped surface when the gate leaf is raised.