An input detection system includes a plurality of electrodes arrayed in a detection region, and an input support device including an LC circuit, a first electrode coupled to the LC circuit and arranged so as to overlap with at least equal to or more than one of the electrodes, and a housing accommodating therein at least the LC circuit. The housing is a conductor, and one end side of the LC circuit is coupled to the housing through a coupling member or a capacitor and another end side of the LC circuit is coupled to the first electrode.