To provide a thermal cutter capable of exhausting dust to appear at a working time by a dust collector, properly at a low cost.

A laser working machine 10 performs a laser processing of a work-piece W on a pallet 31 by irradiating the work-piece W with a laser beam. A frame 80 is equipped, on its inner wall at every exhaust chambers 95a, 95b, 95c and 95d, with a plurality of exhaust ports 96a, 96b, 96c and 96d for providing communications between the exhaust chambers 95a, 95b, 95c and 95d and a duct chamber 90. An average opening area of open holes formed in the exhaust ports 96a, 96b, 96c and 96d is set to become gradually smaller from the exhaust port 96a on the side remotest from a suction port 90a of the duct chamber 90 to the exhaust port 96d on the nearest side.