An ion source having an ion generation container configured to generate ions by reacting ionized gas introduced into the container via a tubular gas introduction pipe with an ion source material emitted in the container. The gas introduction pipe is configured to introduce the ionized gas into an inner space of the gas introduction pipe via a gas supply pipe. In the inner space of the gas introduction pipe, a detachable cooling trap member is disposed and includes a cooling trap portion configured to cool and trap a byproduct produced in the ion generation container. The cooling trap portion is disposed near a supply-side leading end of the gas supply pipe in the inner space of the gas introduction pipe and is not contact with an interior wall face of the gas introduction pipe.