To provide a vacuum pump to easily work in a short period of time while restraining, a bad influence on an environment at the time of constructing an air conditioner.

The vacuum pump makes an air intake port side in a negative pressure state while differential pressure of two chambers gradually damps from initial movable time by dividing the inside of a cylinder into the two chambers by a piston, providing the two divided chambers with suction ports and discharge ports respectively furnished with valve systems, connecting the respective suction ports to each other and actuating the piston in both directions.