A dental x-ray photographing device includes a rotating means (3) for rotating an arm (2) which supports an x-ray source (11) and an x-ray imaging means (12), a sliding means (4) for linearly moving the x-ray imaging means (12). The dental x-ray photographing device obtains a first set of projection images which goes through a first region by moving the x-ray imaging means (12) to a first detection position, obtains a second set of projection images which goes through a second region by moving the x-ray imaging means (12) to a second detection position, and paste the first set of projection images and the second set of projection images together. An origin-position detecting means (5) for detecting an origin position of the x-ray imaging means (12) includes an optical sensor (52) that detects a position of an end (51a) of a light blocking plate that linearly moves together with the x-ray imaging means (12), and detects a time point at which the end (51a) of the light blocking plate passes the optical sensor (52) in the forward direction as the origin position. According to such a configuration, it becomes possible to obtain a highly precise and large FOV using the x-ray imaging means that has a narrow photo receiving surface.
