Abstract: A first inverter logic element, a second inverter logic element, and a third inverter logic element constitute a loop circuit, and a first transistor, a second transistor, and a third transistor are connected between an output of the third inverter logic element and an input of the first inverter logic element. An output signal is taken out from an output of the second inverter logic element, and an oscillation frequency is regulated by the first transistor, the second transistor and the third transistor. Consequently, in a voltage controlled oscillator of the present invention, the number of loop circuits and transistors for regulating the oscillation frequency can be decreased, so that a simulation process can be simplified and required characteristics of the oscillation frequency can be easily obtained.