To perform definite drainage on the job site for an underground structure and also to reduce construction cost.

A drain box 1 capable of definitely carry out drainage of underground water to a shallow swamp 15 and preventing water leakage is embedded in a drain box 1 in constructing the underground structure. At the water- conveyance holes 6 for ground water provided in the surroundings of a drum portion 2 of the drain box 1, stopcocks 8, capable of opening/closing the holes, are installed in the inside. Ground water is able to ingress in a state where the water-conveyance hole is open during the work, and upon the completion of the work, the cock is closed and the underwater pump 5 is made recoverable under the dry state in the drain box 1. After the form 18 is installed and an underground slab is installed, the inside of the box is backfilled, the vicinity of the upper end portion of the box at the trace of removing the from is coated with a water sealing material, and a water leakage from the shallow sump 15 to the top of the underground slab can be prevented surely.