To provide a flap gate with a pivotal structure to a door body that can easily swing even in a small inside and outside water level difference, performs inner water discharge and closing of an opening end advantageously and that can be produced at a low cost, in the flap gate with the door body swinging by an inside and outside water pressure difference in the opening end of a water channel.

A flap gate 10 is provided with a door body 20 for opening and closing an opening end 50 in a water channel, a rotation shaft 30 for swinging the door body 20, nearly V-shaped knife edges 31 installed to project at both ends of the rotation shaft 30, a swing arm 21 supporting the door body 20 and having a groove-shaped bearing part 32 in a recessed column shape and a support fitting 33 supporting the rotation shaft 30. The bearing part 32 pivotally supports the knife edges 31 to constitute a knife edge bearing structure, and the swing arm 21 is installed in the rotation shaft 30. The door body 20 swings freely by the knife edge bearing structure.