A separating device for fluid media receivable in a working housing (1). A separating piston (3) is inside the working housing (1) and separates two media compartments (5, 7) from one another in a media-tight manner. The separating piston (3) is provided along its external circumference with a guide (19). During a transversing movement of the separating piston (3) inside the working housing (1), the guide bears slidably on the housing inner wall (21) and is an integral component of the separating piston (3).