PURPOSE: To continue construction without removing an excavator and a temporary structural base at each time when each floor section of an underground body is built.

CONSTITUTION: In the constructing method of an underground body through a method of caisson construction, a caisson 1 is built and an excavated-soil carrying-out device 11 with an automatic pushing-up mechanism 13 installed to the foundation girder 2 of the caisson 1 is mounted, and the ground of a caisson basement 5 is excavated by the excavated-soil carrying-out device 11 and the caisson 1 is sunk while each floor section 10 of the underground body is constructed onto the foundation girder 2 of the caisson 1. Each floor section 10 is built, the excavated-soil carrying-out device 11 is pushed up by the automatic pushing-up mechanism 13, and the sinking of the caisson 1, the construction of each floor section 10 of the underground body and the pushing-up of the excavated-soil carrying-out device 11 are conducted repeatedly.