[Problem]Provided are an acid addition salt of (+)-2-[(inden-7-yloxy)methyl]morpholine (compound A) and a novel crystal thereof, which are for use as a medicament or a drug substance, and which has high storage stability, particularly high stability against humidity and light.[Means for Solution]An acid addition salt of the compound A with an acid selected from benzenesulfonic acid and hydrobromic acid is a compound which is isolated in the form of a crystal, is a solid at room temperature, exhibits no hygroscopicity at such a level that causes a problem for use as a medicament or a drug substance, has stability against humidity and light, and is therefore extremely useful as a medicament or a drug substance.
