To provide a method and instrument for microcurrent measurement which can measure a microcurrent flowing through a body to be measured sufficiently accurately without increasing the cost.

This is a microcurrent measuring method which measures a microcurrent flowing through the body to be measured by applying a specific voltage to the body to be measured from a measuring instrument; and microcurrents flowing through the body to be measured are measured (S6) at constant intervals of time once a half cycle of a commercial power source in a period corresponding to one cycle or its integral multiple of the commercial power source and their mean value is used as a real measured current value (S13).