Laser machining method

A laser machining method comprising:

• a step of setting a gas pressure on a back surface side of a workpiece to be higher than a gas pressure on a front surface side of the workpiece;
• a step of forming through-holes in the workpiece by irradiating the workpiece with a pulsed laser having a first repetition frequency from the front surface side of the workpiece;
• and
• a finishing step of irradiating inner surfaces of the through-holes with a pulsed laser having a second repetition frequency lower than the first repetition frequency, wherein
• the finishing step is repeated for each of the through-holes by changing only a repetition frequency and by irradiating the inner surface of each of the through-holes with the pulsed laser every time each of the through-holes is formed, to provide the through-holes close to each other,
• in the finishing step of irradiating the inner surfaces of the through-holes with the pulsed laser having the second repetition frequency, a state in which the gas pressure on the back surface side of the workpiece is higher than the gas pressure on the front surface side is continued.