An LC circuit section and a negative resistance section are provided for an LC-VCO. A pair of output terminals are provided for the LC circuit section and an inductor is connected between the output terminals, and two variable capacitors are connected in series to each other parallelly with the inductor. Further, the LC circuit section is provided with a pair of capacitors and a pair of switches that are connected between the capacitors and a ground potential and consist of NMOS transistors. Moreover, a switch that consists of the NMOS transistor is connected between a node, which is between one capacitor and one switch, and a node, which is between the other capacitor and the other switch, and the two nodes are connected to each other when the switch is closed.