ray and masks a portion of the two observed regions referring to fig9 the x ray flat panel detector 1 substantially includes a x ray conversion film and a signal acquisition region 11 which acquires a signal of an operating and tft and an imaging region 12 positioned in an inner portion of the signal acquisition region 11 for carrying out imaging and diagnosis of course the x ray shielding foils 4 of the grid 2 are configured to completely mask the imaging region 12 in addition according to this embodiment the marker 3 is located outside the imaging region 12 but inside a right end of the signal acquisition region 11 with respect to the x ray flat panel detector 1 with respect to the grid 2 the marker 3 is configured and connected to prevent from reaching the above position of the x ray shielding foils 4 but reaches the right end of the top covering material 5 fig1 is a schematic perspective view proximal to the marker 3 to provide more details about the position relationship of fig9 the marker 3 is constituted by a x ray shielding plate 31 and a x ray shielding plate 32 more specifically a material of the x ray shielding plates 31 and 32 includes molybdenum tungsten lead tantalum or an alloy having any of the foregoing elements as a main component which has a larger atomic number and greater x ray absorption therefore when being irradiated.