PURPOSE: To prevent separation and looseness even under strict conditions by piercing wire materials through penetration holes formed in each aligned material board and putting a plurality of material boards together in the form of a plane.

CONSTITUTION: Among a plurality of material boards 2, a material board 2 in the right end is formed with recessions 2A for connecting adjacent material boards 2 and grooves 2B for piercing wire materials 3, and a material board 2 in the left end is formed with protrusions 2C and grooves 2D, and material boards 2 disposed therebetween are formed with recessions 2A and protrusions 2C respectively, and they extend to both upper and lower ends of each material board 2 and connected by fitting these recessions 2A and protrusions 2C each other. Furthermore, in each material board 2, penetration holes 2E are made which communicate to each other in the alignment direction, and wire materials 3 are made to pierce through adjacent penetration holes 2E in turn from for example the upper most penetration hole 2E of the material boards 2 in the right end and then directed downward by way of the grooves 2D and further pierced through the second each penetration hole 2E and groove 2B in the form of zigzag and finally both end parts 3A, 3B thereof are folded so as to be along the grooves 2B. In this state, synthetic resin liquid is infiltrated thereinto and then cured in order to fix the material boards 2 to the wire materials 3.