In this study, we developed an imaging system that can detect polarization modulation with high sensitivity and demonstrated the distribution measurement of a millimeter-wave electric field at 36 GHz by combining it with an electro-optic crystal using the electro-optic (EO) effect. To detect weak polarization changes caused by the birefringence of the EO crystal owing to the EO effect, we proposed a system in which a uniform polarizer is mounted directly above the polarization image sensor. We also developed a system combining an intensity modulator and a booster optical amplifier (BOA) as a local oscillator signal for optical heterodyne and demonstrated the generation of 36 GHz modulated light by DSB-SC modulation at 18 GHz. We performed the electric near-field imaging of a microstrip line at 36 GHz using the fabricated imaging system. We used a (100)-ZnTe crystal as the EO crystal and successfully obtained its intensity and phase distribution.