1. A nuclear medicine diagnosis apparatus comprising: a mechanical collimator for passing through photons having a predetermined energy emitted from an object to be examined into which a drug containing radioactive isotope is injected or dosed, in a predetermined direction; a former-stage detector for detecting positional information at a point of reaction where the photons passed through the mechanical collimator are scattered and information on the momentum of charged particles generated by the reaction; a latter-stage detector disposed in a subsequent stage of the former-stage detector to detect information on the photons having been scattered by the former-stage detector; and image reconstruction means for reconstructing an image from detection information having been collected from the former-stage detector and the latter-stage detector, wherein the image reconstruction means is configured to differentiate the information on the photons having been passed through the mechanical collimator and the information on the photons having been scattered by the former-stage detector, and perform image reconstruction by different image reconstruction algorithms from the individual differentiated detection information.