An apparatus including: a sealing case 20 having a branch-shaped branch hole 23 formed in a first separate case 21 and extending in the radial direction C of an existing pipe 1; and a rubber packing 30 for sealing a gap between the sealing case 20 and the existing pipe 1, wherein: the first separate case 21 is provided with a flange 28 for allowing for attachment and removal of a boring machine 3; the sealing case 20 is capable of reciprocating in the pipe axis direction L; and the rubber packing 30 forms: a first sealed area S1 surrounding a portion of the sealing case 20 where the branch hole 23 is provided for shutting the branch hole 23; and a second sealed area S2 being adjacent to the first sealed area S1, sealed against the first sealed area S1, displaced from the first sealed area S1 in the pipe axis direction L, and sized so as to be able to shut the opening bored by a cutter 3a.