The present invention provides a reagent for measuring a degree of oxidative stress that includes a compound represented by the following general formula (I) or a salt thereof, and a method of measuring a degree of oxidative stress using the reagent for measuring a degree of oxidative stress. In the general formula (I), R1, R2, R3 and R4 each independently represent a hydrogen atom, an ethyl group, an isopropyl group, a hydroxyalkyl group that has 1 to 4 carbon atoms, or a phenyl group, and at least one of R1, R2, R3 or R4 represents an isopropyl group, a hydroxyalkyl group having 1 to 4 carbon atoms, or a phenyl group.