A transdermal administration device comprising: an administration section including a substrate having a first surface and a second surface which is a surface opposite to the first surface, and a projection protruding from the first surface; a first adhesive sheet adhered to the second surface, the first adhesive sheet extending outward from the second surface; a second adhesive sheet adhered to a surface of the first adhesive sheet opposite to a surface which is in contact with the second surface, the second adhesive sheet extending outward from the first adhesive sheet; and a cover which covers the administration section and the first adhesive sheet, wherein the cover includes: a main body that covers the administration section and the first adhesive sheet; and a flange which extends outward from an edge of the main body, the flange being adhered to a portion of the second adhesive sheet which extends outside the first adhesive sheet, and a structure composed of the main body and the flange includes: a remaining portion which includes at least a portion of the flange and is designed to be left on the second adhesive sheet; a tear-off portion which includes at least a portion of the main body and is designed to be separated from the remaining portion; and a tear-off assistance portion which facilitates creation of a cut for separating the tear-off portion from the remaining portion. an administration section including a substrate having a first surface and a second surface which is a surface opposite to the first surface, and a projection protruding from the first surface; a first adhesive sheet adhered to the second surface, the first adhesive sheet extending outward from the second surface; a second adhesive sheet adhered to a surface of the first adhesive sheet opposite to a surface which is in contact with the second surface, the second adhesive sheet extending outward from the first adhesive sheet; and a cover which covers the administration section and the first adhesive sheet, wherein the cover includes: a main body that covers the administration section and the first adhesive sheet; and a flange which extends outward from an edge of the main body, the flange being adhered to a portion of the second adhesive sheet which extends outside the first adhesive sheet, and a main body that covers the administration section and the first adhesive sheet; and a flange which extends outward from an edge of the main body, the flange being adhered to a portion of the second adhesive sheet which extends outside the first adhesive sheet, and a structure composed of the main body and the flange includes: a remaining portion which includes at least a portion of the flange and is designed to be left on the second adhesive sheet; a tear-off portion which includes at least a portion of the main body and is designed to be separated from the remaining portion; and a tear-off assistance portion which facilitates creation of a cut for separating the tear-off portion from the remaining portion. a remaining portion which includes at least a portion of the flange and is designed to be left on the second adhesive sheet; a tear-off portion which includes at least a portion of the main body and is designed to be separated from the remaining portion; and a tear-off assistance portion which facilitates creation of a cut for separating the tear-off portion from the remaining portion.