To provide a voltage-controlled oscillator obtaining an oscillation signal with a comparatively low frequency using neither AGC means nor a semiconductor internal resistance with a simple configuration.

The voltage-controlled oscillator is provided with a switching circuit 5 for inputting a frequency control voltage and an inverse frequency control voltage, and selectively outputting the frequency control voltage or the inverse frequency control voltage corresponding to the output logical state of a switching voltage generator 7; and an integral circuit 6 for integrating the output voltage of the switching circuit 5 to form a triangular signal. The switching voltage generator 7 comprises a reference window voltage generating circuit 7(1) for generating two level window voltages; a window comparison circuit 7(2) for supplying the two level window voltages, and the triangular signal, outputting the first voltage when the triangular signal level is between two level window voltages, and outputting the second voltage in the other cases; and a logic circuit 7(3) for not changing output logic state at the time of output of the first voltage, and changing output logic state at the time of output of the second voltage. The triangular signal of the oscillation frequency proportional to the frequency control voltage is output from the integrator circuit 6.