PURPOSE: To adjust the horizontal deviation of a stowing case opening from a floor opening, by a method wherein a connecting frame board is fastened onto each inside of holding pieces provided along the inner periphery of floor-reinforcing joists located on the periphery of the floor opening, and a flange-shaped connecting frame is fastened onto the lower end part of the connecting frame board.

CONSTITUTION: On a floor 10 over the position where a storing case body 1 is placed, a floor opening 11 is formed, and its position is opposed to a storing case opening 2 therefor. After that, the periphery of the floor opening 11 is reinforced with floor- reinforcing joists 13. After that, an outer frame 14 is fitted into the floor opening 11 from above, and holding pieces 3 each are placed on the undersurface of the outer frame 14 and are fastened onto the floor-reinforcing joists 13, following which a connecting frame board 4 is put inside the holding pieces 3 and is fastened with screws. On the periphery of the lower end part of the connecting frame board 4, a connecting frame 5 is fastened, of which the inner size is smaller than the effective opening size of the storing case opening 2 and of which the outer size is larger than that. In this way, the position of connecting frame board 4 and the connecting frame 5 is adjusted to the floor opening 11.