PURPOSE: To expand the space under the floor and to improve the anti-seismic property by providing horizontal spring members in two directions crossing square each other, between the four corners of an anti-seismic floor and a foundation.

CONSTITUTION: An anti-seismic floor 1 which consists of a free access floor 10, pedestals 11, and a holder 12 is held by an anti-seismics holding device 8 with no horizontal restoring function. Then, between the parts near the four corners of the floor 1, and a foundation 2, horizontal spring members 4 are installed in the directions crossing square each other. Then, linear guides slidable only in the direction square to the axes of the springs 4 are provided to prevent the extension and contraction of the springs 4 in the oblique directions so as to prevent a separation of the spring force from the axial direction. Furthermore, when the holding device 8 furnishes a vertical spring member 13, the springs 4 are installed in the oblique direction to make the space between the floor 10 and the holder 12 wider. As a result, the underfloor cable housing space can be expanded, and the horizontal anti-seismic property can be improved.