A capacitive sensor comprising: a plurality of electrodes (21-ij) each of which is configured to output an electrical signal corresponding to a capacitance determined by a distance between a surface of the capacitive sensor and an electrical conductor, and a processing unit, wherein the plurality of electrodes include first electrodes having a first parasitic capacitance that occurs between the first electrode and a surface of the capacitive sensor and second electrodes having a second parasitic capacitance different from the first parasitic capacitance, that occurs between the second electrode and the surface of the capacitive sensor, the first electrodes and the second electrodes being arranged opposed to the surface of the capacitive sensor in a prescribed pattern that is an alternating line pattern or a checkerboard pattern different than a pattern of biometric information of a body part that is a fingerprint or a palm print to be read by the capacitive sensor, and the processing unit is configured to generate an image in which each of the plurality of electrodes corresponds to one pixel and each pixel has a pixel value proportional to an electrical signal output from a corresponding one of the plurality of electrodes; extract from the image a foreground region which is a region that contains pixels at each of which an electrical conductor is located at a distance capable of forming a capacitor with a corresponding one of the plurality of electrodes; calculate correlation between the foreground region and a filter that matches the prescribed arrangement pattern, values of the filter being different between the first electrodes and the second electrodes, and detect a non-biometric region formed by a non-biometric electrical conductor adhering to a sensor surface of the capacitive sensor based on the calculated correlation of each pixel of the foreground region; and calculate a metric that decreases as the area that the non-biometric region occupies in the foreground region increases, and outputs the image if the metric is higher than a predefined threshold value but discards the image if the metric is not higher than the predefined threshold value. a plurality of electrodes (21-ij) each of which is configured to output an electrical signal corresponding to a capacitance determined by a distance between a surface of the capacitive sensor and an electrical conductor, and a processing unit, wherein the plurality of electrodes include first electrodes having a first parasitic capacitance that occurs between the first electrode and a surface of the capacitive sensor and second electrodes having a second parasitic capacitance different from the first parasitic capacitance, that occurs between the second electrode and the surface of the capacitive sensor, the first electrodes and the second electrodes being arranged opposed to the surface of the capacitive sensor in a prescribed pattern that is an alternating line pattern or a checkerboard pattern different than a pattern of biometric information of a body part that is a fingerprint or a palm print to be read by the capacitive sensor, and the processing unit is configured to generate an image in which each of the plurality of electrodes corresponds to one pixel and each pixel has a pixel value proportional to an electrical signal output from a corresponding one of the plurality of electrodes; extract from the image a foreground region which is a region that contains pixels at each of which an electrical conductor is located at a distance capable of forming a capacitor with a corresponding one of the plurality of electrodes; calculate correlation between the foreground region and a filter that matches the prescribed arrangement pattern, values of the filter being different between the first electrodes and the second electrodes, and detect a non-biometric region formed by a non-biometric electrical conductor adhering to a sensor surface of the capacitive sensor based on the calculated correlation of each pixel of the foreground region; and calculate a metric that decreases as the area that the non-biometric region occupies in the foreground region increases, and outputs the image if the metric is higher than a predefined threshold value but discards the image if the metric is not higher than the predefined threshold value.