A mold having an inner space to which molten steel is injected, comprising a body having the inner space, wherein an inner surface (if) of the body, which heads toward the inner space, comprises a first inclined surface (sf 1) that is inclined to be gradually away from an outer surface (of) opposite to the inner surface (if) in a downward direction and a second inclined surface (sf 2) that is disposed below the first inclined surface (sf 1) and inclined to be gradually close to the outer surface (of) in the downward direction, wherein the mold comprises a convex member protruding from the inner surface (if) of the body to the inner space, wherein the first inclined surface (sf 1) extends up to a first point (P 1) spaced by a first distance (S 1) from an upper end (P U) of the inner surface (if) of the body, wherein the second inclined surface (sf 2) extends up to a lower end (P L) of the inner surface (if) of the body from a second point (P 2) disposed below the first point (P 1) and spaced by a second distance (S 2) from the upper end (P U) of the inner surface (if) of the body, and wherein each of the first distance and the second distance is less than a height of the body, and wherein the body comprises: a pair of long side members each extending in one direction and facing each other in a direction crossing an extension direction thereof; and a pair of short side members each extending to cross the long side member and facing each other to seal a portion between the pair of long side members, wherein the first and second inclined surfaces (sf1, sf2) are disposed on the inner surface (if) of at least one of the long side member and the short side member, and wherein the convex member protrudes from the inner surface (if) of at least one of the long side member and the short side member to the inner space, and a protruding length of the convex member from the inner surface (if) to the inner space gradually decreases in the downward direction, wherein a width of the convex member is less than that of the body, and wherein the convex member extends up to a third point (P 3) spaced by a third distance (S 3) from the upper end (P U) of the inner surface (if) of the body, wherein the third distance (S 3) is greater than the first distance (S 1) and less than the second distance (S 2). a body having the inner space, wherein an inner surface (if) of the body, which heads toward the inner space, comprises a first inclined surface (sf 1) that is inclined to be gradually away from an outer surface (of) opposite to the inner surface (if) in a downward direction and a second inclined surface (sf 2) that is disposed below the first inclined surface (sf 1) and inclined to be gradually close to the outer surface (of) in the downward direction, wherein the mold comprises a convex member protruding from the inner surface (if) of the body to the inner space, wherein the first inclined surface (sf 1) extends up to a first point (P 1) spaced by a first distance (S 1) from an upper end (P U) of the inner surface (if) of the body, wherein the second inclined surface (sf 2) extends up to a lower end (P L) of the inner surface (if) of the body from a second point (P 2) disposed below the first point (P 1) and spaced by a second distance (S 2) from the upper end (P U) of the inner surface (if) of the body, and wherein each of the first distance and the second distance is less than a height of the body, and wherein the body comprises: a pair of long side members each extending in one direction and facing each other in a direction crossing an extension direction thereof; and a pair of short side members each extending to cross the long side member and facing each other to seal a portion between the pair of long side members, wherein the first and second inclined surfaces (sf1, sf2) are disposed on the inner surface (if) of at least one of the long side member and the short side member, and wherein the convex member protrudes from the inner surface (if) of at least one of the long side member and the short side member to the inner space, and a protruding length of the convex member from the inner surface (if) to the inner space gradually decreases in the downward direction, wherein a width of the convex member is less than that of the body, and wherein the convex member extends up to a third point (P 3) spaced by a third distance (S 3) from the upper end (P U) of the inner surface (if) of the body, wherein the third distance (S 3) is greater than the first distance (S 1) and less than the second distance (S 2). a pair of long side members each extending in one direction and facing each other in a direction crossing an extension direction thereof; and a pair of short side members each extending to cross the long side member and facing each other to seal a portion between the pair of long side members, wherein the first and second inclined surfaces (sf1, sf2) are disposed on the inner surface (if) of at least one of the long side member and the short side member, and wherein the convex member protrudes from the inner surface (if) of at least one of the long side member and the short side member to the inner space, and a protruding length of the convex member from the inner surface (if) to the inner space gradually decreases in the downward direction, wherein a width of the convex member is less than that of the body, and wherein the convex member extends up to a third point (P 3) spaced by a third distance (S 3) from the upper end (P U) of the inner surface (if) of the body, wherein the third distance (S 3) is greater than the first distance (S 1) and less than the second distance (S 2).