A disclosure is made of a subterranean connecting method and a connecting apparatus therefor which are suitable for use when two shield machines are used to excavate a pair of tunnel sections from both ends of a tunnel, and the tunnel sections are connected to each other in mid course. During underground connection, it is important to secure sealing and water retarding with respect to soil and water pressure exerted by the ground in the vicinity of the connecting section. For this purpose, in the connecting apparatus, a penetration ring is arranged in one of the shield machines, and a penetration chamber in which the penetration ring is accommodated is arranged in the other shield machine. Both the both shield machines face each other with a slight gap remaining therebetween and, subsequently, the penetration ring is moved forward and penetrates into the penetration chamber of the mating shield machine. By this penetration, the area between both the shield machines are closed by the penetration ring. In this condition, both the shield machines are disassembled, and the wall surface of the connecting section including the penetration ring is covered, so completing the subterranean connecting step. According to the connection using such a penetration ring, sealing and water retarding with respect to the soil and water pressure in the vicinity of the connecting section can be secured.