A radiation imaging system is provided. The system includes radiation imaging apparatuses having an arrangement capable of detecting a start of radiation irradiation, and comprising an output unit to output a first signal representing that the apparatus itself has detected a start of irradiation and a receiving unit to receive a second signal representing that another apparatus has detected the start. In a case in which the start of irradiation is detected in a first state, the apparatus transitions to a second state for generating the image data and outputs the first signal. The apparatus in the second state generates the image data regardless of reception of the second signal. In a case in which the second signal is received in the first state, the apparatus transitions to a third state in which power consumption is lower than the first state.