A capacitance detection device of a capacitance system includes: a capacitance sensor electrode for detecting a capacitance; a power source for supplying charges to be charged in the capacitance sensor electrode; an electric charge storage capacitor in which an amount of charges to be charged therein changes according to the electric charges charged in the capacitance sensor electrode; and a switch for changing a reference potential of the electric charge storage capacitor. The reference potential of the electric charge storage capacitor is changed in a period of measuring the capacitance.