Abstract: A choline salt crystal of (1S)-1,5-anhydro-1-[5-(azulen-2-ylmethyl)-2-hydroxyphenyl]-D-glucitol which shows an endothermic peak at 194 to 198° C. as measured by differential scanning calorimetry (DSC analysis) and shows main peaks at about 2? (°) 5.58, 14.72, 16.80, 17.82, 21.02, and 22.46 as measured by X-ray powder diffraction. Thus, a crystal of an azulene compound can be produced which is in a single crystal form, has a constant quality, can be produced with good reproducibility, can be provided stably as a crystal of an drug substance for use in the preparation of a pharmaceutical and is excellent in storage stability.