Abstract: In a laser plasma X-ray device for use in generating X-rays by bombarding a target material by a pulsed laser beam, the target material is selected from materials which are in a gas phase at the room temperature and which are cooled in a selected one of liquid and solid phases. Such a selected phase of the target material is continuously supplied to a focal point of the pulsed laser beam to be subjected to bombardment and to generate the X-rays. On generation of the X-rays, the target material is rendered into the gas phase to be recycled into the selected phase. The X-rays are guided outside of the chamber through an X-ray gate unit opened in synchronism with a repetition frequency of the pulsed laser beam.