A sensor capable of measuring a plurality of measuring items quickly and accurately, a measuring device, and a measuring method are provided. The sensor includes a sample-holding unit for holding a sample containing an analyte; a sample-supplying port for supplying the sample to the sample-holding unit; a detecting unit for carrying out an electrochemical measurement, the unit being provided in the sample-holding unit; an optical measuring unit for carrying out an optical measurement, the unit being provided in the sample-holding unit; and a reagent-holding unit for holding a reagent for the optical measurement, the unit being provided in the sample-holding unit; wherein in the flowing direction of the sample supplied from the sample-supplying port in sample-holding unit, the sample-supplying port, the detecting unit, and the reagent-holding unit are positioned in the order recited.