To provide a fiberboard having heat accumulation properties utilizable as a building interior material arranged so as to be pasted on the indoor side surfaces such as the wall, ceiling, floor or the like of a house to keep a comfortable room temperature for a long time even if heat preliminarily accumulated by a cooling and heating instrument or natural energy is gradually radiated to generate a large change in the open air temperature.

This heat accumulating fiberboard is obtained by the thermal pressure bonding molding of a composition comprising microcapsules including a heat accumulating material, woody fibers and an adhesive. The film of the microcapsules preferably comprises a thermosetting urea/formalin resin or a melamine/formalin resin and the volume mean particle size thereof is preferably 10 μm or less. The heat accumulation material preferably has a melting point of 5-50°C and can be utilized as a building interior material for stabilizing a room temperature.