To provide a phase information detection method and a phase information detector, capable of acquiring easily phase information of a phase object in real time, without using an expensive phase-contrast microscope.

Light from an image of the phase object is passed through an objective lens having a chromatic aberration, and is image-focused thereafter in a different position depending on a wavelength of the light. A plurality of picked-up images is obtained by picking up the image of the phase object in a position with an equal distance from the objective lens, as to the plurality of wavelengths different each other. The plurality of picked-up images is image-processed to obtain the phase information of the phase object. Brightness is corrected in the image processing, as to each of the plurality of picked-up images, to obtain a plurality of brightness-corrected images. A difference between the brightness-corrected images is found to obtain a brightness difference image as the phase information.