Abstract: In a sensor used in an energy harvesting system, electric power generated by a solar cell module is more efficiently utilized. In a sensor (100), a resistor (3) is connected in parallel with one of a first solar cell module (1a) and a second solar cell module (1b) that have mutually different current-voltage characteristics in the same illuminance environment and in series with the other one of the first solar cell module (1a) and the second solar cell module (1b). A first voltmeter (4a) measures a voltage (V1) across the first solar cell module (1a), and a second voltmeter (4b) measures a voltage (V2) across the second solar cell module (1b). A load (6) is fed with the electric power generated by the first solar cell module (1a) and the second solar cell module (1b).