A radiation irradiation initiation detection apparatus includes an acquisition unit, an averaging unit, a calculation unit and a determination unit. The acquisition unit acquires a detection result for each of frames from a detection section that detects radiation. The averaging unit averages the detection results of a plural number of frames, which detection results have been previously acquired by the acquisition unit. The calculation unit calculates at least one of a difference or a ratio between the most recent detection result acquired by the acquisition unit and an averaging result from the averaging unit. The determination unit determines whether or not irradiation of radiation has been initiated on the basis of calculation results from the calculation unit.
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