An electrostatic coupling type contactless electric power supply device of this present invention comprising: an electrode for electric power supply and a high-frequency power source section provided on a fixed section, an electrode for electric power reception and a received electric power converting section provided on a movable section, and a resonance inductor forming a series resonant circuit, wherein it further comprises: a voltage detection means that detects the traveling wave voltage of the traveling wave from the high-frequency power source section to the series resonant circuit and in the reverse direction the reflected wave voltage of the reflected wave provided between the high-frequency power source section and the series resonant circuit, an auxiliary voltage detection means that detects in a contactless manner the received voltage generated at the electrode for electric power reception provided on the fixed section, and a calculation control means that calculates the load side impedance based on the traveling wave voltage and the reflected wave voltage, determines the resonance state based on the received voltage, and variably controls at least the output frequency or output voltage of the high-frequency power source section. From this, the operating stability of the current consumer on the movable section is higher while being able to simplify the electric circuit on the movable section side, and this can be smaller and lighter, which contributes to reducing the supplied electric power and lowering equipment costs.