The invention provides a radiation irradiation device that can appropriately manage the residual capacity of a battery without being influenced by the internal resistance of the battery. The radiation irradiation device includes a radiation generating part that generates radiation; a battery part that supplies electric power to the radiation generating part; and a residual capacity calculation part that calculates the residual capacity of the battery part. The residual capacity calculation part calculates the residual capacity of the battery part on the basis of a current flowing into the battery part, an internal resistance of the battery part, and a voltage of the battery part.