Compounds of the general formula (I) or salts thereof and activators of PPAR&dgr; (peroxisome proliferator activated receptor &dgr;) containing the compounds or the salts as the active ingredient: wherein R1 and R2 each are hydrogen, C1-8 alkyl, an aryl or heterocyclic group which may be substituted, or the like; A is oxygen, sulfur, or the like; X1 and X2 are each a free valency, oxygen, S(O)p (wherein p is an integer of 0 to 2), C(═O), C(═O)NH, NHC(═O), CH═CH, or the like; Y is optionally substituted C1-8 alkylene; Z is oxygen or sulfur; R3 and R4 are each optionally substituted C1-8 alkyl; and R8 is hydrogen or C1-8 alkyl, with the proviso that when X1 is a free valency, X2 is not O or S(O)p, while when X1 is C(═O)NH, X2 is not a free valency.