The present invention provides a carbostyril compound represented by GeneralFormula (1) or a salt thereof, wherein A is a direct bond, a lower alkylenegroup, or a lower alkylidene group； X is an oxygen atom or a sulfur atom； R4and R5 each represent a hydrogen atom； the bond between the 3 and 4 positionsof the carbostyril skeleton is a single bond or a double bond； R1 is ahydrogen atom, etc； R2 is a hydrogen atom, etc； and R3 is a hydrogen atom,etc. The carbostyril compound or salt thereof of the present invention inducesthe production of TFF, and thus is usable for the treatment and/or preventionof disorders such as alimentary tract diseases, oral diseases, upperrespiratory tract diseases, respiratory tract diseases, eye diseases, cancers,and wounds.
