The central axis of a source head and an extraction electrode is aligned on a line, and confirmed by a laser beam whether the line is coaxial with the ion beam axis. Thus, a light emitting unit that emits the laser beam on the ion beam axis is fitted to a housing instead of the source head, and a reflector that reflects the laser beam is fitted to the extraction electrode. A light emitting apparatus also has a function of detecting the laser beam to detect the laser beam that is reflected by the reflector, and sends the intensity of the detected laser beam to a control unit. The extraction electrode is positionally adjusted so that the intensity of the laser beam becomes maximum, whereby the ion beam axis can coincide with the central axes of the ion source and the extraction electrode.