The present invention aims to provide a parallax detecting apparatus (3) and the like which is capable of suppressing the degree of parallax detection error even in the case of using cameras each having a lens whose resolution is low for the pitch of the pixels of the imaging devices. The parallax detecting apparatus (3) which calculates a parallax that occurs between optical systems includes: a PSF approximating unit (5) configured to modify at least one of images obtained from the respective optical systems such that point spread functions of the optical systems are made to sufficiently approximate a point spread function of a predetermined optical system; and a parallax calculating unit (9) configured to calculate the parallax that occurs between the optical systems, using the image modified by the PSF approximating unit (5).