An oversampling A/D converter with a few operational amplifiers is configured using a complex second-order integrator including first and second second-order integrators and first and second coupling circuits configured to couple these integrators together. Each of the second-order integrators includes an operational amplifier, four resistance elements, and three capacitance elements. The first coupling circuit cross-couples one of two serially-connected capacitance elements inserted between the inverted input terminal and output terminal of the operational amplifier in the first second-order integrator to the counterpart in the second second-order integrator using two resistance elements. The second coupling circuit cross-couples the other capacitance element in the first second-order integrator to the counterpart in the second second-order integrator using two resistance elements.