Abstract: A plurality of sensor circuits each including an oscillator circuit, a detection electrode, and a ceramic resonator for changing a resonance frequency in accordance with a change in small electrostatic capacitance detected by the detector electrode and outputting a detection signal corresponding to a change in resonance frequency are formed on a circuit board. Detector electrode surfaces A.sub.1 to A.sub.4, B.sub.1 to B.sub.4, and C.sub.1 to C.sub.4 of the first to third sensor circuits are formed on the upper surface of the circuit board in a divisional manner. The detection surfaces of the respective sensor circuits are arranged to have codes in the scanning direction of an object to be detected. The fixed capacitances of the detection surfaces are decreased, and a change of state of the object can thus be detected at a high resolution.