A radiographic imaging device comprising: a sensor portion configured to generate an output signal according to an irradiated amount of irradiated radiation; a detection means (32A, 38, 55,99) configured to detect, based on the output signal, a radiation irradiation start of radiation irradiated from a radiation source during capture of a radiographic image when a level of an electric signal generated based on the output signal has exceeded a threshold value; a noise data generation means configured to generate, based on an output signal from the sensor portion in a non-irradiation state of radiation from the radiation source, noise data relating to noise incorporated in the output signal; a control means (17, 97B, 98) configured to control detection sensitivity to radiation irradiation start in the detection means according to a degree of variation in noise level expressed by the noise data, and to lower detection sensitivity to radiation irradiation start in the detection means by setting the threshold value higher the greater the variation in the noise level expressed by the noise data; and an imaging means configured to capture the radiographic image after radiation irradiation start has been detected by the detection means (32A, 38, 55), characterized in that the detection means (32A, 38, 55) includes a charge amplifier (92, 92') that includes a capacitor configured to accumulate charge output as the output signal from the sensor portion, and that is configured to generate an electric signal according to a charge amount accumulated in the capacitor; and the control means (17, 97B, 98) is configured to make a charge accumulation duration of the capacitor longer the greater the noise level variation expressed by the noise data. a sensor portion configured to generate an output signal according to an irradiated amount of irradiated radiation; a detection means (32A, 38, 55,99) configured to detect, based on the output signal, a radiation irradiation start of radiation irradiated from a radiation source during capture of a radiographic image when a level of an electric signal generated based on the output signal has exceeded a threshold value; a noise data generation means configured to generate, based on an output signal from the sensor portion in a non-irradiation state of radiation from the radiation source, noise data relating to noise incorporated in the output signal; a control means (17, 97B, 98) configured to control detection sensitivity to radiation irradiation start in the detection means according to a degree of variation in noise level expressed by the noise data, and to lower detection sensitivity to radiation irradiation start in the detection means by setting the threshold value higher the greater the variation in the noise level expressed by the noise data; and an imaging means configured to capture the radiographic image after radiation irradiation start has been detected by the detection means (32A, 38, 55), characterized in that the detection means (32A, 38, 55) includes a charge amplifier (92, 92') that includes a capacitor configured to accumulate charge output as the output signal from the sensor portion, and that is configured to generate an electric signal according to a charge amount accumulated in the capacitor; and the control means (17, 97B, 98) is configured to make a charge accumulation duration of the capacitor longer the greater the noise level variation expressed by the noise data.