To easily and quickly mount or demount an X-ray film cassette by providing a support member containing a horizontal support part and a vertical support part installed on a baseplate, and combining it with the horizontal support part by almost vertically arranging its vertical support part to one surface of the baseplate.

A holder contains a baseplate 1 and a support member 2, and the support member 2 is composed of a horizontal support part 21 and a vertical support part 22. This horizontal support part 21 is arranged almost in parallel to one surface 10 of the baseplate 1, and the vertical support part 22 is almost vertically arranged to one surface 10 of the baseplate 1, and is combined with the horizontal support part 21. A supporting recessed groove to receive an X-ray film cassette is composed of recessed grooves 210 and 220 arranged in the lengthwise direction of the horizontal support part 21 and the vertical support part 22. In the case of X-ray photographing, after the X-ray film cassette- installed holder 4 is arranged so as to be opposed to an X-ray photographing device 6 by sandwiching a patient 5, X-rays 61 are irradiated toward the patient 5 from the X ray photographing device 6.