Provided is a method of machining a sealing surface, the method being capable of finishing a sealing surface at low cost and in a short period of time, eliminating lead marks, and forming the sealing surface highly accurately. The method of machining a sealing surface comprises finishing a sealing surface (M), which is to be machined, by cutting the sealing surface (M) using a rotating cutting tool (81) while rotating a workpiece having the sealing surface (M) about an axis thereof. The cutting of the sealing surface (M) using the rotating cutting tool (81) comprises hardened steel cutting which generates no lead marks.