To sufficiently shorten a construction period and reduce construction cost as a whole by substantially rationalizing and saving labor for work of arranging reinforcements, erect forms and place concrete at a job site.

For sequentially constructing the prescribed length of an underground structure made of reinforced concrete having internal space along a lengthwise direction under the application of the open cut construction method, ground is excavated from the surface thereof and a foundation work is implemented for the base thereof. Also, an inner form 15 made of precast concrete is used for forming the inner contour of the underground structure. For this construction method, the inner form 15 is placed on leveling concrete 20, and a movable outer form 22 for forming the outer contour of the structure is laid outside a prefabricated reinforcement 15. Then, concrete is placed in space between the inner and outer forms 15 and 22, thereby forming the underground structure. After the placed concrete is cured, a new inner form 15 is laid on the leveling concrete 20 at a position forward of the cured concrete, and the movable outer form 22 is moved to the outside of the inner form 15.