The present invention provides a tetomilast crystal that is industrially easily produced in a large volume. (1) a tetomilast hydrate crystal having a powder X-ray diffraction spectrum having characteristic peaks at 2¸ = 10.6°, 12.9°, 21.1°, 22.3° and 25.0°； (2) an anhydrous tetomilast type C crystal having a powder X-ray diffraction spectrum having characteristic peaks at 2¸ = 4.2°, 8.2°, 12.0°, 16.4°, 24.7° and 25.9°； (3) a tetomilast acetonitrile solvate crystal having a powder X-ray diffraction spectrum having characteristic peaks at 2¸ = 3.6°, 7.1°, 10.6°, 14.2° and 24.8°. These crystals are stable towards heat and moisture, and are also excellent in terms of the disintegration property and dissolution property of tablets. Accordingly, these crystals are preferably used as pharmaceutical compositions.
