An oscillation circuit for generating two oscillation signals having a phase difference of 90° by using an LC oscillator has a disadvantage for integration. Therefore, a differential type ring oscillator comprising interpolation type delay circuits of four stages is used as an original oscillator without using any LC oscillator. The oscillation frequency of the original oscillator is set to f/2. Intermediate signals S(k) having a phase difference of 45(k−1)° with respect to a reference phase are obtained as the outputs of the respective stages of the original oscillator. A multiplying circuit 22 generates the product signal of S(2) and S(4) in mixers. This product signal is vibrated at cos (ft/2), and the output signal Vout1 is generated on the basis of the product signal. A multiplying circuit generates the product signal of S(1) and S(3) in mixers. This product signal is vibrated at cos(ft/2+π/2), and the output signal Vout2 is generated on the basis of the product signal. Vout1, Vout2 are output as the oscillation signals having the frequency f and the phase difference of 90°.