To provide a device and a method for laser beam machining for making the taper of the inner face of a via hole smaller and suppressing the thermal influence around the machining part.

The device is provided with a laser oscillator 1 which generates a pulsed laser beam, an optical system 2 for scanning a face to be machined with the pulsed laser beam, and a profile varying means 14 which varies the energy density distribution of the pulsed laser beam. A simultaneous start of machining over the whole diameter of the via hole is prevented by varying the energy density distribution of the pulsed laser beam into a semi-flat distribution 15, and evaporated high temperature gas is so controlled not to flow along a work. Thus via hole machining with a small taper and a small thermal influence is realized.