Abstract: A laser machining apparatus (1) for burning holes in a workpiece has an objective lens (20) which is movable in a plane generally perpendicular to the lens axis to enable the laser beam to be moved and focused at different surface locations on the workpiece (14). This enable clusters of holes to be machined in the workpiece surface without the necessity of moving the workpiece except, perhaps, for horizontal movement which is normally a rotational indexing of the workpiece, the laser beam being horizontally directed. Detection of burn-through of the beam is effected by an optoelectronic detector circuit which monitors the light intensity transmitted from the workpiece surface during burning of a hole by the laser, the light being transmitted back along the laser beam path through a mirror and filter system (18, 38, 44) to the detector circuit. Once burn-through is effected the fall in light intensity is detected by the circuit which triggers movement of either the beam or workpiece or both.