Reactive oxygen species measuring device

2−A reactive oxygen species measuring device according to the present invention comprises a reactive oxygen species sensor provided with an electrode assembly capable of detecting the presence of reactive oxygen species or the like in terms of an electric current, a power source means for applying a measuring voltage to the reactive oxygen species sensor, and a reactive oxygen species concentration measuring means for measuring a concentration of the reactive oxygen species or the like from the current detected by the reactive oxygen species sensor. According to the present invention, a concentration of reactive oxygen species or the like such as in vivo or in vitro superoxide anion radical (O.) can be measured reliably, and the entire device can be formed in a smaller size and always mounted to a living body.