A laser machining apparatus, including: a laser light source; a transparent member that is set on an optical path of a laser beam and transmits the laser beam; a contact type temperature difference sensor, set on a surface of the transparent member outside an irradiation range of the laser beam, for detecting a temperature difference between a surface of the transparent member, which is spaced apart from a center of the transparent member by a first distance, and another surface of the transparent member, which is spaced apart from the center of the transparent member by a second distance larger than the first distance; and a controller correcting a focal position based on the temperature difference detected by the contact type temperature difference sensor to stabilize a beam diameter of the laser beam condensed onto a machining object.