PURPOSE: To measure catalase activity simply and at higher accuracy using the whole blood by arranging a hydrogen peroxide permeable film and an interfering substance separation film on a hydrogen peroxide electrode in the order.

CONSTITUTION: In this catalase activity measuring apparatus, a hydrogen peroxide permselective film 2 and an interfering substance separation film 3 are arranged on a hydrogen peroxide electrode 1 in the order. Blood is spotted on the interfering substance separation film 3 and then, a substrate solution with a known concentration of hydrogen peroxide is spotted. Blood cells or the like in the blood are blocked from permeating diffusively with the separation film 3 to allow the permeation of the blood component alone diffusively. The substrate solution permeates diffusively as intact. After the permeation of the solution, an amount of the hydrogen peroxide corresponding to an activity value of catalase is decomposed in the blood and the amount thereof decreases in correspondence to the activity value of the catalase and time elapsed while the amount of the hydrogen peroxide reaching the surface of the hydrogen peroxide electrode 1 passing through the hydrogen peroxide permselective film 2 reduces likewise. Any interfering substance contained in a specimen passing through the film 3 is blocked with the film 2 to allow the preventing of a drop in the measuring accuracy. Then, a ratio of electrical signals is calculated with an arithmetic section 4 in several sec after the spotting and after a specified time passes and a conversion processing is performed to obtain an activity value of the catalase.