Abstract: The present invention provides a PPAR? activator containing a novel PPAR? agonist (peroxisome proliferator-activated receptor ?) as an active ingredient, and an exercise tolerance-improving agent containing the same as an active ingredient. The present invention is a PPAR? activator containing a guanidine derivative or a biguanidine derivative as an active ingredient, wherein the PPAR? activator activates transcriptional activity of PPAR?, and the guanidine derivative and the biguanidine derivative are capable of fitting within a PPAR? ligand binding pocket in a state where a guanidino group or a biguanidino group forms a hydrogen bond with amino acid residues corresponding to each of the 413th histidine, 287th histidine, 253rd threonine and the 437th tyrosine of human PPAR?, among amino acid residues constituting an interior surface of the ligand binding pocket; and is an exercise tolerance-improving agent containing the PPAR? activator as an active ingredient.