A waveguide-type broadband optical isolator according to the present invention, comprising: a reciprocal phase shifter which makes a phase difference 3π/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 λ, and a nonreciprocal phase shifter which provides a phase difference π/2 for forward propagating waves and a phase difference −π/2 for backward propagating waves.