A shutter piece (3, 3', 203) suitable for a shutter set (1, 201) used in a shutter device suitable to envelop an inner material, which is supplied to a center of a disc-like outer skin material, with a peripheral portion of the outer skin material to form an enveloped food product comprising: a first side surface (13, 213) which includes a convex peripheral edge (13a, 213a) extending from a first base-side point (13b, 213c) to a tip edge (3c, 203c) of the first side surface (13, 213) in a plan view for sealing the peripheral portion of the outer skin material above the inner material, a second side surface (15, 215) which is located below the first side surface (13, 213) and includes a convex protruding edge (15a, 215a) which extends from a second base-side point (15c, 215c) to a tip-side end point (15b, 215b) of the second side surface (15, 215) in the plan view, and a third side surface (17, 217) which is located below the first side surface (13, 213) and defines a portion of a pyramid-like space (17a, 217s) above the inner material when the peripheral portion of the outer skin material is sealed by the first side surface (13, 213), characterized in that the second side surface (15, 215) is defined so as to protrude from the first side surface (13, 213) in the plan view, and the second side surface (15, 215) comprises the second base side point (15c, 215c) located away from the peripheral edge (13a, 213a) of the first side surface (13, 213) in the plan view so that the second side surface (15, 215) in use, contacts the outer skin material earlier than the first side surface (13, 213) so as to centrally gather the outer skin material toward the location above the center of the inner material, and a width between the peripheral edge (13a, 213a) and the protruding edge (15a, 215a) in the plan view becomes narrower from the second base-side point (15c, 215c) toward the tip-side end point (15b, 215b) of the second side surface (15, 215), and the tip-side end point (15b, 215b) is located at a position which is substantially the same as that of the convex peripheral edge (13a, 213a) of the first side surface (13, 213) in the plan view. a first side surface (13, 213) which includes a convex peripheral edge (13a, 213a) extending from a first base-side point (13b, 213c) to a tip edge (3c, 203c) of the first side surface (13, 213) in a plan view for sealing the peripheral portion of the outer skin material above the inner material, a second side surface (15, 215) which is located below the first side surface (13, 213) and includes a convex protruding edge (15a, 215a) which extends from a second base-side point (15c, 215c) to a tip-side end point (15b, 215b) of the second side surface (15, 215) in the plan view, and a third side surface (17, 217) which is located below the first side surface (13, 213) and defines a portion of a pyramid-like space (17a, 217s) above the inner material when the peripheral portion of the outer skin material is sealed by the first side surface (13, 213), characterized in that the second side surface (15, 215) is defined so as to protrude from the first side surface (13, 213) in the plan view, and the second side surface (15, 215) comprises the second base side point (15c, 215c) located away from the peripheral edge (13a, 213a) of the first side surface (13, 213) in the plan view so that the second side surface (15, 215) in use, contacts the outer skin material earlier than the first side surface (13, 213) so as to centrally gather the outer skin material toward the location above the center of the inner material, and a width between the peripheral edge (13a, 213a) and the protruding edge (15a, 215a) in the plan view becomes narrower from the second base-side point (15c, 215c) toward the tip-side end point (15b, 215b) of the second side surface (15, 215), and the tip-side end point (15b, 215b) is located at a position which is substantially the same as that of the convex peripheral edge (13a, 213a) of the first side surface (13, 213) in the plan view.