Upon producing a transparent polycrystalline material, a suspension liquid (or slurry 1) is prepared, the suspension liquid being made by dispersing a raw-material powder in a solution, the raw-material powder including optically anisotropic single-crystalline particles to which a rare-earth element is added. A formed body is obtained from the suspension liquid by means of carrying out slip casting in a space with a magnetic field applied. On this occasion, while doing a temperature control so that the single-crystalline particles demonstrate predetermined magnetic anisotropy, one of static magnetic fields and rotary magnetic fields is selected in compliance with a direction of an axis of easy magnetization in the single-crystalline particles, and is then applied to them. A transparent polycrystalline material is obtained by sintering the formed body, the transparent polycrystalline material having a polycrystalline structure whose crystal orientation is controlled. In this calcination step, after subjecting the formed body to primary sintering at a temperature of 1,600-1,900 K, the resulting primarily-sintered body undergoes hot-isotropic-press sintering (or HIP processing) at a temperature of 1,600-1,900 K.