To provide a laser beam machining apparatus which allows an origin position in laser beam irradiation to coincide with the center of rotation even in a laser beam machining apparatus with a structure where a laser beam can not be moved to the origin position.

The irradiation position of a laser beam is respectively moved to first and second positions having first and second distances from the origin position of laser beam irradiation, after the movement, a machining object OB set in a table 11 is rotated, the machining object OB is irradiated with a laser beam from a machining head 20, and circular first and second machining remains are respectively formed at the machining object OB. The surface of the machining object OB set in the table 11 is photographed with a camera 40, the radii of the circular first and second machining remains are respectively measured, and the displacement of the origin position to the actual center of rotation is calculated using the measured radii of the circular first and the second machining remains and the first and second distances being the distances from the origin position to the laser beam irradiation position.