Dental X-ray image detecting device with an automatic exposure function

A dental X-ray image detecting device to be disposed in an inter-oral region behind a tooth to be photographed, wherein X-rays penetrating the tooth are converted into an optical image and the optical image is then converted into a digital signal to be reproduced on a monitor display, said dental X-ray image detecting device arranged such that an X-ray image sensor comprising a first X-ray fluorescent element, a solid-state image pickup device mounted on a surface of a fixture substrate and a plurality of optical fiber bundles for optically connecting a fluorescent surface of the X-ray fluorescent element to an image pickup surface of the image pickup device, is housed in an outer casing, said dental image detecting device further comprising an X-ray intensity detecting element secured to the surface of the fixture substrate, said detecting element comprising a photo detecting element and a second X-ray fluorescent element mounted on the photo detecting element, wherein cores of filaments of all of the glass fiber bundles are joined substantially perpendicular both to the fluorescent surface of the first X-ray fluorescent element and to the surface of the solid-state image pickup device, each of said bundles having a diameter substantially equal to one another, and a bottom section of said outer casing, located in the X-ray radiation direction from the X-ray fluorescent element, includes an X-ray shield material.