The vacuum generator is capable of quickly and securely holding and releasing a work piece and capable of reducing amount of consuming compressed air. In the vacuum generator, a first nozzle and a second nozzle jet compressed air toward a diffuser nozzle. The second nozzle has a diameter greater than that of the first nozzle. Switching means switches a state of the vacuum generator between a first state, in which a small amount of air sucked from the vacuum port, and a second state, in which a large amount of air is sucked from the vacuum port. The first nozzle, the second nozzle and the diffuser nozzle are serially arranged in that order.