To prevent ground from getting loose by constructing shafts at both sides in a section covered with a thin soil layer and excavating the lower ground with the shielding excavation method, after a pipe roof has been laid by a pipe jacking method between both shafts.

Shafts 6, 7 are excavated at both sides of a main road 1 in order to form a shield tunnel 3 passing through sections A, B covered with a thin soil layer in the underground 2 of the main road 1 and a plurality of steel pipes 8 are extended from the shafts 6, 7 with the pipe jacking method, in the section A, B covered with a thin soil layer to prevent the ground between the shafts 6, 7 from getting loose and form a pipe roof 9. The lower ground 2 is excavated by a shield excavator in the state the upper side is protected by the pipe roof 9. Accordingly, the ground is prevented from getting loose and embedded structures are prevented from being damaged. And it is not necessary to execute the construction work from the ground surface and hence, traffic jams are not brought.