to arrange supplementary members 6 and 7 between the pieces of equipment c and the beams 2 as illustrated in fig1 in the case where the supplementary members 6 and 7 are arranged and the pieces of equipment c are placed on the supplementary members 6 and 7 it is possible to support the pieces of equipment c more stably since the supplementary members 6 are arranged plane symmetric mirror symmetric to the supplementary members 7 the following explanations are focused on the supplementary members 6 the supplementary members 6 transfer the weights of the pieces of equipment c to the beams 2 as illustrated in fig1 the supplementary members 6 are arranged to straddle the first seat members 3 or the second seat members 4 the supplementary members 6 in the present embodiment are formed of an extruded shape of an aluminum alloy as illustrated in fig1 b each of the supplementary members 6 includes a pair of supports 61 and a table portion 62 the supports 61 are respectively arranged on the front and rear sides the supports 61 are arranged on the front and rear sides of the first seat members 3 so as to project from the lower surface of the table portion 62 the supports 61 is arranged to have the same height as the first seat members 3 the upper surface of the table portion 62 abuts the lower surface of one of the pieces of equipment c illustrated in fig1 and the lower surface of the table portion 62 abuts the upper surface of the bolt holder 31 in the first seat members 3 as illustrated in fig1 a the table portion 62 has a planar shape a plurality of elongated adjustment holes 6 a being arrayed in the lateral direction of.