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 that is substantially the same as the powder X-ray diffraction spectrum shown in FIG. 2; (2) an anhydrous tetomilast type A crystal having a powder X-ray diffraction spectrum that is substantially the same as the powder X-ray diffraction spectrum shown in FIG. 4; (3) an anhydrous tetomilast type C crystal having a powder X-ray diffraction spectrum that is substantially the same as the powder X-ray diffraction spectrum shown in FIG. 8; (4) a tetomilast acetonitrile solvate crystal having a powder X-ray diffraction spectrum that is substantially the same as the powder X-ray diffraction spectrum shown in FIG. 10; and (5) a mixture consisting of the above anhydrous tetomilast type A crystal and an anhydrous tetomilast type B crystal. 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.