The invention provides an amine salt of a carbostyril derivative formed from a carbostyril derivative represented by the formula (1) [wherein R is a halogen atom; the substituted position of the side chain is 3- or 4-position in the carbostyril skeleton; and the bonding between 3- and 4-positions of the carbostyril skeleton is a single bond or a double H bond] and an amine; and the invention is useful as drugs for treating various diseases, especially as aqueous formulations due to the superior water solubility and the superior pharmacologic effects.