A low-power voltage controlled oscillator is provided. The voltage controlled oscillator includes (2n+1) first circuit components (n is an integer of one or more). An output terminal of the first circuit component in a k-th stage (k is an integer of one or more and 2n or less) is connected to an input terminal of the first circuit component in a (k+1)-th stage. An output terminal of the first circuit component in a (2n+1)-th stage is connected to an input terminal of the first circuit component in a first stage. One of the first circuit components includes a second circuit component and a third circuit component whose input terminal is connected to an output terminal of the second circuit component. The third circuit component includes a first transistor and a second transistor whose source-drain resistance is controlled in accordance with a signal input to a gate through the first transistor.