A carbostyril derivative and a salt thereof according to the present invention is represented by the following general formula (1), ##STR3## wherein R1 is a hydrogen atom, a lower alkyl group, a lower alkenyl group, a lower alkynyl group or a phenyl-lower alkyl group; R2 is a lower alkanoyl group, a lower alkoxycarbonyl group, a furoyl group, a lower alkanesulfonyl group, a benzoyl group (which ma