An polarization information acquisition unit includes a phase adjuster configured to adjust phases of two linearly polarized components of incident light, which oscillate in directions orthogonal to each other, a detector configured to transmit a polarized component oscillating in one direction and not to transmit a polarized component oscillating in a direction orthogonal to the one direction, the polarized components being included in light emitted from the phase adjuster, and a photoelectric convertor configured to photoelectrically convert a polarized component transmitted through the detector. The phase adjuster has at least three areas. The at least three areas include at least two areas having phase adjusting amounts different from each other, and at least two areas having an identical phase adjusting amounts and having slow axes whose directions are different from each other by 20 to 90 degrees inclusive.