connected to a drain of the transistor m sw2 one terminal of the variable capacitor c var1 is connected to a node na which is a contact point between the drain electrode of the transistor m sw1 and one terminal of the inductor l 1 and the other terminal is connected to one terminal of the variable capacitor c var2 the other terminal of the variable capacitor c var2 is connected to a node nc which is a contact point between the drain electrode of the transistor m sw2 and the other terminal of the inductor l 1 at this time voltage v tune is supplied to the variable capacitors c var1 and c var2 to change values of the capacitors and the frequency of an output signal is changed depending on the changed capacitor value herein the inductor l 1 and the variable capacitors c var1 and c var2 are connected to each other in parallel the drain electrode of the transistor m sw1 is connected to one terminal of the inductor l 1 and a source electrode of the transistor m sw1 is connected to a drain electrode of the transistor m gm1 at this time direct current dc as bias voltage v bias is applied to a gate electrode of the transistor m sw1 and an output terminal.