PURPOSE: To protect a capacitance variable element by providing a resistance between the variable capacitance electrode which sends or receives charges to/from the floating electrode and the semiconductor substrate.

CONSTITUTION: In a variable capacitance element having the floating electrode 13 covered with the insulating layer 12 on the N- type substrate 11, the capacitance electrode (N+ layer) 14 and N- substrate 11 are isolated by the P- layer 16, capacitance variable electrode (N+ layer) 18 and substrate 11 are isolated by the P- layer 17, moreover the poly-Si thin film resistor 19 is provided between the capacitance variable electrode 18 and substrate 11, and the resistor 19 is selected to 10kΩ, thereby even when a longer lead wire is connected to the capacitance variable electrode 18, a high voltage due to inductance or static- electricity is no longer applied. In addition, since a resistor 19 is formed in the insulating film 12 on the substrate 11, it has the same impedance for a positive or negative voltage of electrode 18 and is effective for noise in any diriction. Moreover, it works as a sufficient impedance for capacitance variable voltage in any of the positive and negative direction and is capable of changing impedance. Therefore, it does not change the capacitance value in accordance with noise.