With a delta sigma modulator of this invention, a plurality of clocks required to control a switching circuit can be easily generated and correlation among phases of the plurality of clocks can be automatically maintained while a frequency of the clocks is modified. A ring oscillator is formed of three delay circuits provided with differential amplifiers in the delta sigma modulator. A clock producing circuit produces the plurality of clocks to control the switching circuit by delaying three-phase clocks outputted from the ring oscillator. All the tail currents Ic in the differential amplifiers in the delay circuits in the ring oscillator and the tail currents Ic in the differential amplifiers in the delay circuits in the clock producing circuit are proportional to each other.