The present invention provides a compound, a salt thereof, or a prodrug thereof as a compound effective for preventing and/or treating fibrosis, the compound being represented by formula (1) (wherein A is an optionally substituted benzene ring; B is optionally substituted aryl or optionally substituted heteroaryl; X is an oxygen atom or a sulfur atom; Y is a nitrogen atom or a carbon atom; of Y is a single or double bond when Y is a carbon atom, or of Y is a single bond when Y is a nitrogen atom; each R1 independently represents lower alkyl, or two R1s may be bound to each other to form a spiro ring or a crosslinked structure, or two R1s may be bound to each other to form a saturated fused heterocycle together with nitrogen and carbon atoms constituting a ring containing Y; p is 0, 1, or 2; or (R1)p is oxo).