PURPOSE: To facilitate maintenance, inspection and repair and realize easy installation at an intermediate story and on the roof by elevating a pool movable floor through turning of a rotary shaft, having a turning arm penetrating a pool wall, from the outside of the pool wall.

CONSTITUTION: A turning means 32, for a turning shaft 21 of a turning arm 24, composed of a control panel 33, a geared motor 34 with a brake, a transmission device 35, bearing 37 and the like is installed in an operation room 31 adjacent to a pool 1 with a partition wall 11 in-between. Plural rotary shafts 21 are extended into the pool 1 through water seal bearings 22 equipped in the partition wall 11 and supported by bearings 23 installed on the pool bottom 2. Frames 4 of a floor material 5 of a movable floor 3 are supported from the underneath by rollers 25 at tips of turning arms 24 attached to the rotary shafts 21, and the turning arms 24 are turned by driving the turning means 32 so as to steplessly elevate the movable floor 3 to an optional height.