A 90-degree optical hybrid interferometer having an optical path length difference to a pair of the optical signal waveguide arm and the local oscillator optical waveguide arm at either the I phase side or the Q phase side at the TE optical signal side and the TM optical signal side respectively thus giving a phase delay to output interference signals of the I phase side and the Q phase side. The 90-degree optical hybrid interferometer has eight output ports arranged in order of Ip, In, Qp, and Qn at both the TE side and the TM side respectively, by setting the output phase difference which is the sum of the phase difference according to the optical path length difference and phase conversion characteristics of each optical coupler at the I phase side and the Q phase side and the phase delay, as +π/2.