To prevent direct transmission of a shock wave, which is caused in blasting work carried out on a cutting face, to the outside of a pit (the atmosphere) or to the other main pit through a pilot hole part for preventing a worker working on the outside of the pit, a resident on the periphery, or a worker working in the other main pile from being harmed and preventing a dust collector arranged in the pilot hole part from direct damage in a ventilation system in tunnel construction for constructing a tunnel by cutting and expanding the previously formed pilot hole part to expand the main pit.

In this ventilation system in tunnel construction, in which the main pits 2 and 3 are expanded by cutting and widening the previously formed pilot hole part 1, the dust collector 4 is arranged in the pilot hole part 1, while movable air doors 5 and 6 are arranged on the main pit side at least.