1. A Compton camera device comprising: a pre-stage detector for directly detecting a quantum ray including a cosmic ray and a gamma ray; a post-stage detector for detecting the quantum ray incident to the pre-stage detector and scattered by a Compton scattering phenomenon; image reconstruction means for reconstructing the distribution of the quantum ray detected by the pre-stage detector and the post-stage detector as image information; and display means for displaying the image information subjected to the image reconstruction, the device further comprising: first means for reading coordinate data of a scattering point of the quantum ray detected by the pre-stage detector for each Compton scattering event; second means for reading coordinate data of a reaching point of the Compton-scattered quantum ray detected by the post-stage detector for each Compton scattering event; and third means for calculating a measurement accuracy of the scattered quantum ray by the first and second means for each Compton scattering event, calculating a statistical quantity of the quantum ray for each calculated measurement accuracy, and outputting the calculated statistical quantity to the image reconstruction means.