The present invention relates to a laser beam machining apparatus which enables plural sheets of work to be mounted so as to be simultaneously processed, and which has a small size, even in the case where the number of sheets of work is increased. The laser beam machining apparatus includes a XY table which enables a work to be mounted on a bed of the laser beam machining unit and which is movable in the X and Y axis directions, and a gate-shaped over-frame having a laser irradiation optical system which irradiates a laser beam on the above described work so as to perform drilling or cutting, wherein the above described laser irradiation optical system is supported so as to be movable in the Z axis direction, wherein the bed of the laser beam machining unit is cut out in left and right front portions so as to make installation parts for leg parts of the gate-shaped over-frame left behind, and wherein a work feed unit and a work discharge unit are arranged so as to be inserted into the above described left and right front cutout portions.