To provide an electrostatic capacitance type proximity sensor capable of dispensing with manual re-regulation at each fluctuation of sensitivity or precision caused by a change in a size or a material of a detection object, or a change accompanied by the lapse of time in a component, and operable over a long period of time even if detecting a liquid face of a small amount of chemical liquid put into a container formed of an insulator such as glass and a synthetic resin.

This electrostatic capacitance type proximity sensor is provided with a means for controlling a bias voltage of a variable capacity diode by a micro processor or the like by assembling the variable capacity diode in a resonance circuit comprising electrostatic capacitance and inductance generated between a detecting electrode and the object, and a voltage-to-capacitance characteristic diagram of the variable capacity diode formed into data for the micro processor to be referred, finds the maximum and minimum electrostatic capacitance of the object causing detection by observing phases of an excitation voltage and a resonance voltage, and controls average electrostatic capacitance so as to be brought into the electrostatic capacitance of the variable capacity diode when operated.