Crystal polymorphism may exist in a crystalline compound. In the case where crystal polymorphism exists, depending on the crystal form, solubility, dissolution rate, 5 stability against heat, light, humidity, etc. or the like is different. Accordingly, in the production of a pharmaceutical product, it is a very important task to select a crystal form of a drug substance most suitable for a disease indication and a dosage form. The present invention relates to novel crystal forms (A crystal, W crystal, and a hydrate crystal (H crystal)) of a compound I having a strong opening action with respect to 10 KCNQ2-5 channels.
