A voltage-controlled oscillator comprising: an active element for oscillation for amplifying power in the voltage-controlled oscillator; and tuned circuits (12a, 12b, 12c, 12d, 12e, 12f) connected to at least three locations out of six locations, the locations consisting of: a first location corresponding to a first terminal of the active element for oscillation, a second location corresponding to a second terminal of said active element, a third location corresponding to a third terminal of said active element, a fourth location between the first terminal and second terminal and connected to both, a fifth location between the second terminal and third terminal and connected to both, and a sixth location between the third terminal and first terminal and connected to both, wherein said at least three tuned circuits are connected to the first, second and third terminals respectively, wherein a load resistance is connected to at least one of said three or more tuned circuits (12a, 12b, 12c, 12d, 12e, 12f), for outputting oscillation power amplified by said active element for oscillation; wherein variable-capacitance elements (15a, 15b, 15c) are provided to said three or more tuned circuits each, and vary their capacitances in response to a control voltage, wherein an inductor (14a, 14b, 14c) is provided to each of said three or more tuned circuits (12a, 12b, 12c), and is connected to the variable-capacitance element in series in each tuned circuit as series resonant circuit (12a, 12b, 12c), and wherein the variable-capacitance element is composed of a varactor diode, wherein said tuned circuits (12a, 12b, 12c, 12d, 12e, 12f) feed part of the amplified power back to the active element for oscillation, and the active element for oscillation further amplifies the power, and wherein, to control the oscillation frequency of the oscillator, the control voltages applied to the variable-capacitance elements (15a, 15b, 15c) are varied. an active element for oscillation for amplifying power in the voltage-controlled oscillator; and tuned circuits (12a, 12b, 12c, 12d, 12e, 12f) connected to at least three locations out of six locations, the locations consisting of: a first location corresponding to a first terminal of the active element for oscillation, a second location corresponding to a second terminal of said active element, a third location corresponding to a third terminal of said active element, a fourth location between the first terminal and second terminal and connected to both, a fifth location between the second terminal and third terminal and connected to both, and a sixth location between the third terminal and first terminal and connected to both, wherein said at least three tuned circuits are connected to the first, second and third terminals respectively, wherein a load resistance is connected to at least one of said three or more tuned circuits (12a, 12b, 12c, 12d, 12e, 12f), for outputting oscillation power amplified by said active element for oscillation; wherein variable-capacitance elements (15a, 15b, 15c) are provided to said three or more tuned circuits each, and vary their capacitances in response to a control voltage, wherein an inductor (14a, 14b, 14c) is provided to each of said three or more tuned circuits (12a, 12b, 12c), and is connected to the variable-capacitance element in series in each tuned circuit as series resonant circuit (12a, 12b, 12c), and wherein the variable-capacitance element is composed of a varactor diode, wherein said tuned circuits (12a, 12b, 12c, 12d, 12e, 12f) feed part of the amplified power back to the active element for oscillation, and the active element for oscillation further amplifies the power, and wherein, to control the oscillation frequency of the oscillator, the control voltages applied to the variable-capacitance elements (15a, 15b, 15c) are varied. a first location corresponding to a first terminal of the active element for oscillation, a second location corresponding to a second terminal of said active element, a third location corresponding to a third terminal of said active element, a fourth location between the first terminal and second terminal and connected to both, a fifth location between the second terminal and third terminal and connected to both, and a sixth location between the third terminal and first terminal and connected to both, wherein said at least three tuned circuits are connected to the first, second and third terminals respectively, wherein a load resistance is connected to at least one of said three or more tuned circuits (12a, 12b, 12c, 12d, 12e, 12f), for outputting oscillation power amplified by said active element for oscillation; wherein variable-capacitance elements (15a, 15b, 15c) are provided to said three or more tuned circuits each, and vary their capacitances in response to a control voltage, wherein an inductor (14a, 14b, 14c) is provided to each of said three or more tuned circuits (12a, 12b, 12c), and is connected to the variable-capacitance element in series in each tuned circuit as series resonant circuit (12a, 12b, 12c), and wherein the variable-capacitance element is composed of a varactor diode, wherein said tuned circuits (12a, 12b, 12c, 12d, 12e, 12f) feed part of the amplified power back to the active element for oscillation, and the active element for oscillation further amplifies the power, and wherein, to control the oscillation frequency of the oscillator, the control voltages applied to the variable-capacitance elements (15a, 15b, 15c) are varied.