A radiation imaging apparatus, comprising: a flat panel detector; a holding unit for holding at least the flat panel detector; and an arithmetic operation unit and a power supply control unit for controlling a power-supplying to the flat panel detector, wherein the flat panel detector is configured to be connectable and disconnectable from the holding unit, for enabling performing connecting state radiographing with the flat panel detector connected to the holding unit, and non-connecting state radiographing with the flat panel detector disconnected from the holding unit, characterized in that the arithmetic operation unit and the power supply control unit are configured to change a power supplied to the flat panel detector between a first power and a second power, so as to perform, at the first power, the connecting state radiographing generating a heat quantity of the flat panel detector larger than a heat quantity of the flat panel detector generated in the non-connecting state radiographing, and to perform, at the second power, the non-connecting state radiographing generating a heat quantity of the flat panel detector smaller than the heat quantity of the flat panel detector generated in the connecting state radiographing, wherein, the flat panel detector performs, at the second power, the non-connecting state radiographing controlled by the arithmetic operation unit and the power supply control unit such that power consumption of the flat panel detector in the non-connecting state radiographing is lower than power consumption of the flat panel detector in the connecting state radiographing, and performs, at the first power, the connecting state radiographing controlled by the arithmetic operation unit and the power supply control unit such that power consumption of the flat panel detector in the connecting state radiographing is higher than power consumption of the flat panel detector in the non-connecting state radiographing. a flat panel detector; a holding unit for holding at least the flat panel detector; and an arithmetic operation unit and a power supply control unit for controlling a power-supplying to the flat panel detector, wherein the flat panel detector is configured to be connectable and disconnectable from the holding unit, for enabling performing connecting state radiographing with the flat panel detector connected to the holding unit, and non-connecting state radiographing with the flat panel detector disconnected from the holding unit, characterized in that the arithmetic operation unit and the power supply control unit are configured to change a power supplied to the flat panel detector between a first power and a second power, so as to perform, at the first power, the connecting state radiographing generating a heat quantity of the flat panel detector larger than a heat quantity of the flat panel detector generated in the non-connecting state radiographing, and to perform, at the second power, the non-connecting state radiographing generating a heat quantity of the flat panel detector smaller than the heat quantity of the flat panel detector generated in the connecting state radiographing, wherein, perform, at the first power, the connecting state radiographing generating a heat quantity of the flat panel detector larger than a heat quantity of the flat panel detector generated in the non-connecting state radiographing, and to perform, at the second power, the non-connecting state radiographing generating a heat quantity of the flat panel detector smaller than the heat quantity of the flat panel detector generated in the connecting state radiographing, wherein, the flat panel detector performs, at the second power, the non-connecting state radiographing controlled by the arithmetic operation unit and the power supply control unit such that power consumption of the flat panel detector in the non-connecting state radiographing is lower than power consumption of the flat panel detector in the connecting state radiographing, and performs, at the first power, the connecting state radiographing controlled by the arithmetic operation unit and the power supply control unit such that power consumption of the flat panel detector in the connecting state radiographing is higher than power consumption of the flat panel detector in the non-connecting state radiographing.