A radiation irradiation device is provided that includes: a metal target that emits bremsstrahlung X-rays as a radiation beam due to irradiation with an electron beam a radiation shielding member that includes a slit-shaped radiation passage portion and that is disposed downstream of the metal target in the radiation beam emission direction and is disposed such that a portion of the radiation beam passes through the radiation passage portion and the radiation beam incident to regions other than the radiation passage portion is blocked and an electron beam generating device that irradiates, onto the metal target, an electron beam such that a diameter at a generation point of the emitted radiation beam is smaller than a length of an entry portion of the radiation passage portion along a length direction of the entry portion.
