According to one embodiment, a laser ion source is configured to generate ions by application of a laser beam, the laser ion source including a case to be evacuated, an irradiation box disposed in the case and including a target which generates ions by irradiation of laser light, an ion beam extraction mechanism which electrostatically extracts ions from the irradiation box and guides the ions outside the case as an ion beam, a valve provided to an ion beam outlet of the case, the valve being opened at ion beam emission and being closed at other times, and a shutter provided between the valve and the irradiation box, the shutter being intermittently opened at ion beam emission and being closed at other times.