To prevent erroneous detection in detecting a foreign matter, which is caused by a change in distance between a sample and an X-ray detector, provided is an X-ray transmission inspection apparatus including an X-ray tube (11) that irradiates an inspection sample element with an X-ray, an X-ray detector (13) that detects a transmission X-ray when the X-ray is transmitted through a sample, an operation portion (17) that obtains a contrast image from a transmission image of a transmission X-ray, a sensor that calculates a distance between the sample and the detector, and a mechanism that adjusts the position of the X-ray detector, in which an X-ray transmission image is picked up while the distance between the sample and the X-ray detector is kept constant.