An X-ray imaging apparatus comprising a scintillator panel which converts an X-ray emitted from an X-ray generator into visible light; an image detector which includes a plurality of pixels arranged in a matrix, and charges the plurality of pixels with electric charges proportional to intensity of the visible light converted by the scintillator panel; a gate driver which selects a line of the image detector and applies a drive signal to pixels of the selected line; an automatic exposure request signal generator which detects the X-ray emitted from the X-ray generator and generates an automatic exposure request signal; and a controller which verifies validity of the automatic exposure request signal upon receiving the automatic exposure request signal from the automatic exposure request signal generator, and controls a time point for exposure operation according to states of the drive signal when it is determined that the automatic exposure request signal is valid; characterized in that the X-ray imaging apparatus comprises a plurality of automatic exposure request signal generators, wherein the automatic exposure request signal generators of the plurality of automatic exposure request signal generators are disposed at locations corresponding to a middle portion and corners of the image detector, and the controller determines that the automatic exposure request signal is valid when receiving automatic exposure request signals, the number of which is more than or equal to a reference number, from the plurality of the automatic exposure request signal generators, and wherein the automatic exposure request signal generators comprise: a light to electric signal converter, wherein the light to electric signal converter consists of: a light converter which converts the X-ray emitted from the X-ray generator into the visible light and a light detector which detects the visible light converted by the light converter and converts the visible light into an electric signal; and a light detector which detects visible light converted by the scintillator panel and converts the visible light into an electric signal or an X-ray detector which detects an X-ray emitted from the X-ray generator and converts the X-ray into an electric signal; and wherein the automatic exposure request signal generators further comprise: an amplifier which amplifies the electric signal converted by the light detector or by the X-ray detector; and a trigger conversion circuit which converts the electric signal amplified by the amplifier into a digital signal and generates the automatic exposure request signal; and an offset compensator which compensates for an offset of the amplifier to maintain the electric signal amplified by the amplifier to be less than or equal to a threshold voltage. a light converter which converts the X-ray emitted from the X-ray generator into the visible light and a light detector which detects the visible light converted by the light converter and converts the visible light into an electric signal; and a light detector which detects visible light converted by the scintillator panel and converts the visible light into an electric signal or an X-ray detector which detects an X-ray emitted from the X-ray generator and converts the X-ray into an electric signal; and wherein the automatic exposure request signal generators further comprise: an amplifier which amplifies the electric signal converted by the light detector or by the X-ray detector; and a trigger conversion circuit which converts the electric signal amplified by the amplifier into a digital signal and generates the automatic exposure request signal; and an offset compensator which compensates for an offset of the amplifier to maintain the electric signal amplified by the amplifier to be less than or equal to a threshold voltage. an amplifier which amplifies the electric signal converted by the light detector or by the X-ray detector; and a trigger conversion circuit which converts the electric signal amplified by the amplifier into a digital signal and generates the automatic exposure request signal; and an offset compensator which compensates for an offset of the amplifier to maintain the electric signal amplified by the amplifier to be less than or equal to a threshold voltage.