A flap gate comprising: a rotation bearing adapted to be provided at an opening (E) of a structure (W); a substrate adapted to be provided at the bottom of the opening (E); a flapping door configured to flap with respect to the substrate ; and a watertight elastic sheet for ensuring water tightness between the flapping door and the substrate , characterized by the rotation bearing comprising: a housing adapted to be disposed at the bottom of the opening (E); a door base disposed at the flapping door of the flap gate , wherein the watertight elastic sheet is disposed on a top surface of the door base ; a first rotating member rotationally supported by the housing via a first shaft ; a second rotating member rotationally supported by the housing via a second shaft having an axis being different from the axis of the first shaft ; a synchronizing member rotationally connected to the first rotating member and the second rotating member so as to synchronize rotations of the first rotating member and the second rotating member ; and connecting members that rotationally connect the door base to the first rotating member and the second rotating member with different axes , wherein, when the flapping door is laid flat, a pivot of the flapping door is at a higher position than the axes for rotationally connecting the connecting members to the door base , the pivot being located near or in the watertight elastic sheet . a rotation bearing adapted to be provided at an opening (E) of a structure (W); a substrate adapted to be provided at the bottom of the opening (E); a flapping door configured to flap with respect to the substrate ; and a watertight elastic sheet for ensuring water tightness between the flapping door and the substrate , characterized by the rotation bearing comprising: a housing adapted to be disposed at the bottom of the opening (E); a door base disposed at the flapping door of the flap gate , wherein the watertight elastic sheet is disposed on a top surface of the door base ; a first rotating member rotationally supported by the housing via a first shaft ; a second rotating member rotationally supported by the housing via a second shaft having an axis being different from the axis of the first shaft ; a synchronizing member rotationally connected to the first rotating member and the second rotating member so as to synchronize rotations of the first rotating member and the second rotating member ; and connecting members that rotationally connect the door base to the first rotating member and the second rotating member with different axes , wherein, when the flapping door is laid flat, a pivot of the flapping door is at a higher position than the axes for rotationally connecting the connecting members to the door base , the pivot being located near or in the watertight elastic sheet . a housing adapted to be disposed at the bottom of the opening (E); a door base disposed at the flapping door of the flap gate , wherein the watertight elastic sheet is disposed on a top surface of the door base ; a first rotating member rotationally supported by the housing via a first shaft ; a second rotating member rotationally supported by the housing via a second shaft having an axis being different from the axis of the first shaft ; a synchronizing member rotationally connected to the first rotating member and the second rotating member so as to synchronize rotations of the first rotating member and the second rotating member ; and connecting members that rotationally connect the door base to the first rotating member and the second rotating member with different axes , wherein, when the flapping door is laid flat, a pivot of the flapping door is at a higher position than the axes for rotationally connecting the connecting members to the door base , the pivot being located near or in the watertight elastic sheet . <EOS>