the pipe 210 coaxial with the laser capillary 201 is arranged outside the laser capillary 201 therefore a plurality of parallel cooling water channels are constituted by spaces each of which is formed by the adjacent two heat radiation fins 209 the laser capillary 201 and the pipe 210 the cooling water channels are connected to each other at both the end portions of the laser capillary 201 which have no partitions formed by the heat radiation fins 209 cooling water is supplied from a common inlet port 211 and the cooling water is exhausted from a common outlet port 212 reference numeral 202 and 203 denote a discharge path and a feedback path in this embodiment since the heat radiation fins are in contact with the laser capillary 201 over its entire length an air cooling effect which is more excellent than that of the first embodiment can be obtained in these embodiments the internal mirror laser apparatuses have been described however the present invention is not limited to these embodiments the present invention can be applied to a so called external mirror laser apparatus having a pair of brewster bulbs arranged at both the ends of the laser apparatus the laser apparatus of the present invention can be operated by selecting any one method from three types of cooling means i e an air cooling method using an air cooling fan a water cooling method for causing cooling water to pass through a channel and a cooling method using both of the air cooling method and the water cooling method therefore in the laser apparatus according to the present invention when.