A sealed honeycomb structure comprising: a honeycomb structure having porous walls dividedly forming a plurality of cells extending from an end surface of an inlet side to an end surface of an outlet side, the plurality of cells being a plurality of fluid channels; an outlet side sealing portion mounted at openings of predetermined cells in the end surface of the outlet side so as to form inlet cells where the end surface of the inlet side is open and the end surface of the outlet side is sealed; and an inlet side sealing portion mounted at openings of remaining cells in the end surface of the inlet side so as to form outlet cells where the end surface of the outlet side is open and the end surface of the inlet side is sealed, wherein at least one cell among the outlet cells is a reinforced cell where a reinforcing part for reinforcing the outlet cell is formed at at least one corner portion at which the walls on a cross-section vertical to an extending direction of the cell cross each other, wherein all the inlet cells are non-reinforced cells where the reinforcing part is not formed at all the corner portions at which the walls on the cross-section vertical to the extending direction of the cell cross each other, wherein the reinforcing parts of the reinforced cells are formed at a section of the honeycomb structure from the end surface of the outlet side of the honeycomb structure in the extending direction of the cell, and wherein a length of the reinforcing part in the extending direction of the cell is larger than or equal to a length of the outlet side sealing portion in the extending direction of the cell, characterized in that the reinforcing part is formed on the section corresponding to a range smaller than or equal to 1/3 of the length of the honeycomb structure in the extending direction of the cell from the end surface of the outlet side of the honeycomb structure. a honeycomb structure having porous walls dividedly forming a plurality of cells extending from an end surface of an inlet side to an end surface of an outlet side, the plurality of cells being a plurality of fluid channels; an outlet side sealing portion mounted at openings of predetermined cells in the end surface of the outlet side so as to form inlet cells where the end surface of the inlet side is open and the end surface of the outlet side is sealed; and an inlet side sealing portion mounted at openings of remaining cells in the end surface of the inlet side so as to form outlet cells where the end surface of the outlet side is open and the end surface of the inlet side is sealed, wherein at least one cell among the outlet cells is a reinforced cell where a reinforcing part for reinforcing the outlet cell is formed at at least one corner portion at which the walls on a cross-section vertical to an extending direction of the cell cross each other, wherein all the inlet cells are non-reinforced cells where the reinforcing part is not formed at all the corner portions at which the walls on the cross-section vertical to the extending direction of the cell cross each other, wherein the reinforcing parts of the reinforced cells are formed at a section of the honeycomb structure from the end surface of the outlet side of the honeycomb structure in the extending direction of the cell, and wherein a length of the reinforcing part in the extending direction of the cell is larger than or equal to a length of the outlet side sealing portion in the extending direction of the cell, characterized in that the reinforcing part is formed on the section corresponding to a range smaller than or equal to 1/3 of the length of the honeycomb structure in the extending direction of the cell from the end surface of the outlet side of the honeycomb structure.