To provide a vacuum pump allowing an air conditioner to be easily and rapidly installed while suppressing an adverse effect on an environment when the air conditioner is installed.

In this vacuum pump, the inside of a cylinder 15 is divided into an upper chamber 15A and a lower chamber 15B through a piston 16, and the piston is connected to a handle 18 operating the piston through a support shaft 17 disposed on the upper chamber side. The vacuum pump comprises an intake port 20a where a check valve 20 is disposed at the top dead center of the upper chamber and an exhaust port 19a where a check valve 19 is disposed. An opening port 21 allowing intake and exhaust is provided in the lower chamber of the cylinder. After the upper chamber is brought into a negative pressure state by operating the piston downward, the piston is moved upward by an intake action from the opening port.