An infrared sensor includes a series capacitor element and a reference capacitor element each exhibiting a predetermined capacitance value; an infrared-detecting capacitor element whose capacitance value varies depending on an intensity of infrared light incident on the element; and an output node being a node at which a first terminal of the series capacitor element, a first terminal of the reference capacitor element and a first terminal of the infrared-detecting capacitor element are connected to one another. The intensity of infrared light is output as a potential difference between the reference potential which is brought to a potential by applying a predetermined voltage between the series capacitor element and the reference capacitor element and the detection potential which is brought to a potential by applying a predetermined voltage between the series capacitor element and the infrared-detecting capacitor element.