A waveguide-type broadband optical isolator according to the present invention, comprising: a reciprocal phase shifter which makes a phase difference 3.pi./2 between a first light wave propagating through a first waveguide and a second light wave propagating through a second waveguide, with a fundamental operating wavelength .lamda., and a nonreciprocal phase shifter which provides a phase difference .pi./2 for forward propagating waves and a phase difference -.pi./2 for backward propagating waves.