To acquire a radiation dose distribution or radiation intensity distribution with high precision in the longitudinal direction even for a deformed long body to be measured.

This radiation measuring device is provided with a plurality of radiation detectors 3 arranged along the longitudinal direction and detecting the radioactive rays emitted from the long measured body 1, distance detectors 5 measuring the distances between the radiation detectors 3 and the surface of the body to be measured 1 in the direction perpendicular to the longitudinal direction, and an arithmetic circuit 7 correcting the detection results detected by the radiation detectors 3 based on the distances measured by the distance detectors 5 between the radiation detectors 3 and the surface of the body 1 in the direction perpendicular to the longitudinal direction and calculating the radiation dose distribution or radiation intensity distribution in the longitudinal direction of the body 1 based on the corrected detection results.