In a laser machining system, gas is injected while air is inducted from the rear of a plurality of injection nozzles (9c) disposed in the space between the machining head (3) and the workpiece (M) and disposed at stipulated intervals in the direction in which the laser light passes, so as not to disturb the machining gas, thus preventing the adhesion of dust arising during laser machining to optical components (31, 32) within the head (3). A light receptor (4) that receives light reflected or dispersed due to adhered contamination is disposed upstream of the optical components (31, 32) within the head (3), and a determination part (6) compares the light reception value against a preset threshold value.