Provided are a measuring method for the degree of degradation of lubricating oil, and a measuring device therefor, such that (a) acidity is measured using a hydrogen ion-induced type ISFET, and (b) dielectric constants or capacitances at two or more frequencies are obtained, that the degradation state of the lubricating oil is assessed on the basis of the aforementioned acidity and the aforementioned dielectric constants or capacitances, that thereby the degree of degradation of the lubricating oil can be easily and accurately measured, and that the mechanism of the aforementioned degradation can be predicted.