There is provided a lightweight plaster board having a cellular porous plaster core, excellent in adhesion to a covering base paper for a plaster board, free from dry-out in side edge parts of the plaster board, and with no disadvantage in workability for driving a nail into the plaster board. The plaster board includes a plaster core having a front surface, a back surface, and four side surfaces, and at least one covering base paper that covers the front surface, the back surface, and the at least two opposite side surfaces of the plaster core. The plaster core includes one or more hard edge parts each including one of the side surfaces covered with the covering base paper, one or more high-density parts including the front surface or the back surface, not including the side surface covered with the covering base paper, and having a density substantially equal to the density of the hard edge part, and a low-density part having a density less than the densities of the hard edge part and the high-density part and contacting with the hard edge part and the high-density part. The hard edge part does not include a position in which a nail is driven.