In utilizing photocurrent generated in the photoexcitation of a dye in specific detection of an analyte, highly accurate detection can be realized by discharging charged current generated in the formation of a sensor unit and, in the detection of photocurrent of a plurality of detection spots provided on a working electrode, discharging photocurrent which is derived from a detection spot subjected to the latest photocurrent measurement and becomes noise current. The present invention provides a measuring apparatus comprising a sensor unit comprising a working electrode, a counter electrode, and an electrolyte-containing substance, a single or plurality of light sources that apply light to the working electrode, an XY moving device provided when the light source is moved relatively in an XY direction relative to the working electrode, an ammeter that measures current which flows across the working electrode and the counter electrode, and a discharge device that discharges charged current and photocurrent derived from a detection spot subjected to the latest photocurrent measurement. The specific detection method using the measuring apparatus is carried out by controlling the timing of light irradiation and the timing of connection to the ammeter and the discharge device.