PROBLEM TO BE SOLVED: To provide a radiation image photographing device 1 which can precisely detect irradiation start of radiation even in a case when irradiation time of the radiation is short like in photographing of a newborn infant.SOLUTION: Detection means 22 of a radiation image photographing device 1 is constituted to detect irradiation start of radiation when it is determined that there is a possibility that the irradiation of the radiation is continuously started in acquisition processing of an object value dleak for the prescribed number of times. Detection processing of the irradiation start of the radiation is simultaneously performed in parallel under a plurality of conditions including the condition that a first prescribed number of times, which is set for regular photographing, is set as the prescribed number of times, and a second prescribed number of times, which is set for the prescribed number of times, which is smaller than the first prescribed number of times. When the irradiation start of the radiation is detected in at least one detection processing in the respective detection processing performed under the plurality of conditions, the irradiation of the radiation is detected to be started.
