PROBLEM TO BE SOLVED: To prevent liquid metal from spilling in the circumference of a target forming part when a liquid metal target forming device is started or stopped.SOLUTION: A bellows 17 is connected to a nozzle 11 and the nozzle 11 is supported by a movement support part 13. When liquid lithium is ejected from the nozzle 11, the nozzle 11 is moved to allow the distal end to be inserted to a reception part 12. When a liquid metal target forming device is started in this state, liquid lithium is ejected from the nozzle 11 and directly input to the reception part 12. After the ejection becomes stable, the nozzle 11 is separated from the reception part 12 to expose a target T. The target T is irradiated with a proton beam B. When the device is stopped, the nozzle 11 is moved again to be inserted to the reception part 12, and the device is stopped. Consequently, liquid lithium is prevented from spilling from a portion between the nozzle 11 and the reception part 12 when the device is started or stopped.
