The present invention provides A PPARγ activator comprising a butenolide compound represented by the formula (1) or a pharmaceutically acceptable salt thereof:wherein R1 represents a hydrogen atom, a phosphate group, a fatty acid group, an alkyl group having 1 to 4 carbon atoms and optionally having a substituent or a sugar residue optionally having a substituent, and R2 represents a phenyl group, a methylphenyl group, a dimethylphenyl group, an ethylphenyl group, a benzyl group, a methylbenzyl group, a dimethylbenzyl group, an ethylbenzyl group, a phenethyl group, a methylphenethyl group, a dimethylphenethyl group, or an ethylphenethyl group.
