To provide a drift correcting device capable of minimizing laser beam drift on the surface of an object to be irradiated and also to provide a laser beam machine using this device.

The drift correcting device 6 of a laser beam machine 1 is provided with a laser generator 20 equipped with a pair of reflection mirrors 28, 29 forming an optical resonator, a beam shaping unit 23a for converting a laser beam from the generator 20 to a beam with a narrow cross sectional shape, a detector 32, 33 for detecting the center position in the width direction of the beam passed through the beam shaping unit 23a, and an orientation controlling mechanism 34, 35, 36, 37 which, in the case where the detecting center position P deviates by the drift of the beam, changes the orientation θf, θr of at least one reflection mirror of the optical resonator so as to eliminate the deviation ΔP.