A liquid supply mechanism is disposed on an upper portion of a holding unit of a laser processing apparatus. The liquid supply mechanism includes: a liquid chamber having a transparent plate positioned such that a gap is formed between the transparent plate and the top surface of a workpiece held on a holding table; a linear-motion mechanism configured to linearly move the transparent plate over the liquid chamber; a liquid supply nozzle configured to supply a liquid from one side of the liquid chamber to the gap; and a liquid discharge nozzle configured to discharge the liquid from another side of the liquid chamber. A laser beam irradiating unit includes a laser oscillator configured to irradiate the workpiece through the transparent plate and the liquid supplied to the gap.