A laser processed hole is formed in a workpiece. The workpiece has a first member formed of a first material bonded to a second member formed of a second material. A value is set representing the minimum number of shots of a pulsed laser beam when the spectral wavelength of plasma has changed from the spectral wavelength inherent in the first material to that of the second material. A maximum shot number is set representing a maximum value of the number of beam shots when the spectral wavelength of the plasma has completely changed. The beam is stopped if the number of shots has reached the minimum value and the spectral wavelength of the plasma has changed whereas the beam is continued until the number of shots reaches the maximum value if the spectral wavelength of the plasma has not changed even after the number of shots has reached the minimum value.