PURPOSE: To measure glucose or the like accurately by using a dye pair containing 3-methyl-2 benzotiazolinon hydrozone(MBTH) and 8-anilino-1- naphthalene sulphonate(ANS) as the indicator.

CONSTITUTION: As the indicator in a stage reaction for forming strong oxidizing agent, a dye pair containing MBTH and ANS is used. The strong oxidizing agent reacts with the dye pair and forms the blue dye. MBTH and ANS are soluble into aqueous solution but become insoluble when oxidizing coupling is performed. The MBTH-ANS dye pair indicates the intense and flat spectrum absorption in the region of about 600-650nm. In this region, there is no interference of blood color. Thus, other analysis material, which reacts with glucose and oxidase and forms the strong oxidizing agent, can be accurately measured by using a LED optical element. For example, a hole 16 is provided in the region having a reagent pad 10 of a plastic holder 12, and the reagent is applied on one side of the pad through the hole 16. The light is directed on the pad 10 from a light source 18, and the reflected light is measured by a detector 20.