The present invention refers to a key cutting machine for the 10 duplication of keys, in particular of so-called 'laser-type' keys, comprising a mechanical machining unit (1) connected to an electronic control unit (2) that is provided with memory means for storing the coded data of the keys to be duplicated, in which said mechanical machining unit comprises, along with a tracer or key follower (15) for tracking the bit notch pattern of 15 the keys to be duplicated, a spindle (13) and a milling cutter (14) associated thereto, both said cutter and said spindle being adapted to be driven rotatably about the axis thereof, as well as a carriage (5) on which there is mounted a jaw (9), said carriage being movable on the base-plate (4) of the mechanical machining unit in a plane that is orthogonal to the 20 plane of the milling cutter and the key follower or tracer. Said milling cutter (14) is temporarily attached to the end portion of a stem (18) that is adapted to be inserted axially in said spindle (13) through the back-side end portion of the latter, so as to enable said milling cutter to be fastened to said end portion of the same spindle. The milling cutter 25 (14) is adapted to be brought into contact with a reference plane on the jaw (9) so as to directly and readily achieve a correct setting and adjustment of the milling cutter (14) itself in the operating position thereof.