A laser beam machining head comprises a first machining head section having a flange in a first end part in a direction along an optical axis direction of laser light and having a laser light emission nozzle in a second end part, a second machining head section having an engaged part engaged with the above-mentioned flange of the first machining head section for detachably holding the above-mentioned first machining head section, and an O ring being engaged in an engagement part placed in an outer peripheral surface of the above-mentioned flange opposed to an inner peripheral surface of the above-mentioned engaged part and pressed against the inner peripheral surface of the above-mentioned engaged part, whereby when the first machining head section collides with an obstacle, a breakage prevention function reliably operates for preventing not only damage to the first machining head section, but also damage to the whole laser beam machining head, and in the normal state, the first machining head section is held and fixed reliably.