PURPOSE: To perform optimum correction for hardening of radiation quality and obtain a reconstituted image of good quality by comparing a radiation attenuation quantity distribution obtained from radiation absorption data of every projection direction or its integral value with the last radiation attenuation quantity distribution or integral value.

CONSTITUTION: The radiation tomographic inspecting device has a BH auxiliary correcting device 12-3 which perform the best auxiliary correction of an X-ray absorption value with an X-ray beam having an attenuation quantity τ after the correction for hardening of radiation quality, and an optimum X-ray attenuation quantity is obtained by correcting the attenuation quantity τ by the auxiliary correction coefficient (g) (τ), thereby equalizing S1 and S2 in area. Namely, X-ray absorption data after the correction for hardening of radiation quality is multiplied by the coefficient (1+Kθg(τ)) consisting of the auxiliary correction coefficient g(τ) and a coefficient Kθ depending upon the projection direction θ of X rays to the cross section of an object body in an shape of point asymmetry to equalize S2 and Sn to each other, thereby obtaining an image of good quality.