PURPOSE: To provide the title casting apparatus constituted so as to uniformize the distribution of particles of silica, cement or the like.

CONSTITUTION: A casting port 5 has an opening part having an oblong shape and the opening part is arranged in the vicinity of the bottom plate 1a of a mold 1. The opening part has regions almost equally divided into three regions in the length direction thereof and the opening area of each of both left and right regions is set to about 1.2-1.9 times that of the central region. By this constitution, the difference of stirring force between the slurry flowing through the central part in the mold and the slurries flowing along both left and right side walls 1b of the mold is reduced and the sedimentation of particles of silica or cement is reduced and lightweight areated concrete uniformized in particle distribution is obtained.