PURPOSE: To contrive the facilitation of fixing a bundle in a double floor by laying a floor plate through the bundle on a base, fixed to a floor surface, while position adjusting the bundle thereafter fixing it to a base plate.

CONSTITUTION: A base plate 1 is provided, and small protrusions 11 of reverse dish shape, having a bolt hole 12, are formed in several places. Next a bottom plate 21 is provided in a bundle 2, and an insertion hole 22 a little larger by several mm to 30mm than a bolt diameter is formed corresponding to a position of the bolt hole 12, while a supporting leg 23 is vertically provided in the center. Then after a bolt 13 is inserted into each hole 12 from the bottom surface side, the plate 1 is secured to a floor surface 3. The bolt 13 is inserted into the hole 22, and a plate 21 is temporarily placed on the plate 1 and position- adjusted, then execution work of a floor plate is performed on the bundle 2. While as necessary, a cushion panel unit 4 is provided. Further the plate 21 is fixed to the plate 1 by a nut. In this way, the necessity for preliminary setting out is eliminated, and after an upper part structure is set up, the bundle can be easily fixed to the floor surface.