To manufacture a fiber board with a large width and prevent a grainlike pattern from disappearing even when a flaw generated on the surface is repaired by shaving, in the manufacture of the fiber board with the grainlike pattern.

This grainlike pattern is obtained by mixing a thermoplastic fiber 50a with a natural fiber 50b to form a bandlike light color mat 50 and mixing a thermoplastic fiber 51a with a natural fiber 51b to form a bandlike thick color mat 51 and further lapping both mats 50, 51 together to obtain a bandlike laminated mat 52. These laminated mats 52 are obliquely lapped over each other while the laminated mats 52 are shifted, to form a multiple laminated mat 53. Next this multiple laminated mat 53 is compressed in the thickness direction, while it is heated, into a fiber board. The multiple laminated mat 53 is formed by sending the bandlike laminated mats 52 onto a moving transport conveyor 31 while the laminated mats 52 are moved reciprocally in a direction crossing the conveyance direction of the transport conveyor 31. Thus the mats are transferred onto the transport conveyor 31 in such a state that the mats 52 are folded to the specified width.