There is provided an X-ray nondestructive testing device which irradiates X-rays to an article, the article including a substrate having a predetermined X-ray absorption coefficient and a measurement target object disposed therein and having another X-ray absorption coefficient differing from that of the substrate, the device including: an X-ray source configured to irradiate the X-rays to the article; a detector configured to detect the transmission amounts of the X-rays passed through the article at at least paired different locations; a detection position specifying designator configured to specify the paired different locations as a set of paired locations based on a pre-stored design information; a driving mechanism configured to move the detector to the set of paired locations; and an operation calculator configured to calculate the thickness of the measurement target object based on the transmission amounts of the X-rays detected by the detector.