Processing of transmissive material 1 by the laser beam LB, a state contacting the light absorbing layer 2 on the processed surface of the transmissive material 1, the laser beam to be processed surface of the transmissive material 1 through the light absorbing layer 2 It is carried out by irradiating the LB. When irradiating the pulsed laser beam LB having a predetermined energy several times intermittently, along with machined hole depth of the light absorbing layer 2 with the repetition of the laser beam irradiation is gradually increased to the through hole 2a is formed bottom diameter of the through hole 2a is gradually expanded. Further, machined hole depth energy absorbed in the light absorbing layer 2 is converted into heat in the process of the lower end diameter of the process and the through hole 2a is gradually enlarged gradually increased, transmissive material 1 and the light absorbing layer 2 the size and depth of the hole 1a with the drilling is started gradually increases with respect to the processing surface of the transmissive material 1 by heat generated at the interface BF with.