Damage of a rotor and a side plate are suppressed with a simple construction to prevent reduction in durability of a vacuum pump. A casing manufacturing method comprises a step (step S2) of disposing a cylinder liner forming a cylinder chamber in a mold, and casting a casing main body integrally with the cylinder liner by using molten metal, and a step (step S3) of processing an intercommunication hole and an exhaust hole so that the intercommunication hole and the exhaust hole penetrate through both the cylinder liner and the casing main body together and intercommunicate with the cylinder chamber.