A manhole cover apparatus is provided to make drainage capacity and backflow capacity equal by opening an opening to the maximum with a pair of flaps and to have excellent drainage and backflow functions with low expenses. A manhole cover apparatus comprises a container provided with a hanging projection, an opening(121) formed on the bottom of the container, and an opening and closing device opening and closing the opening. The opening and closing device comprises composed of a first plate(88a) and a second plate(88b) installed at two sides to be rotatable on a rotary shaft fixed to the container to make the first plate opened together with the second plate simultaneously by drain pressure applied on the upper side of the second plate in case of draining and to make the second plate opened by deadweight after the first plate is opened by backflow pressure applied on the rear side of the first plate in case of flowing backward, and at least one or more flap stoppers(90) installed to the container to restrict the rotation angle of the flap.
