A machining apparatus for laser machining a workpiece in a machining zone is provided, having an interface for a machining laser source for generating a machining laser beam with a direction of propagation; an outlet opening for the machining laser beam; and an optical system between the interface and the outlet opening, wherein the optical system has: at least one optical unit that adjusts the focal length of the optical system, and at least one stationary laser beam guiding device with at least one movable surface, wherein the at least one movable surface can be adjusted such that it modifies the focal length of the optical system and/or the beam parameter product of the machining laser beam integrated over time in at least one operating mode. Further provided is a method for laser machining a workpiece.