PURPOSE: To efficiently construct the floor section of a pool.

CONSTITUTION: An erect wall section 2 is provided on the periphery of concrete foundation 1 to form a pool substrate 3. Long support members 5 are arranged in parallel at a required interval in the width direction of the pool on the right portion and the left portion across the center portion in the longitudinal direction of the pool. The upper faces 21 of the support members 5 are inclined according to the water gradient of the floor face of the pool to be formed. Floor panels are supported on adjacent support members 5, and the floor panels are fixed to the support members 5.