1. An X-ray image photographing apparatus having: a photographing portion having an image obtaining portion for obtaining a distribution of X-ray having transmitted through an object, and can mount a grid unit including at least a grid for removing scattered rays from the object; a grid detection system for obtaining information from said grid unit or by using said grid unit, and detecting at least one of presence or absence of the grid, a kind of the grid and presence or absence of replacement of the grid; and a control portion for executing photographing or image processing on the basis of at least the result of the detection by said grid detection system.