A laser beam irradiation apparatus includes an oscillation unit, an acousto-optic deflection unit for deflecting a laser beam oscillated by the oscillation unit, a condenser for condensing the deflected laser beam, and a control unit. The control unit determines an actual output power of the laser beam based on a light reception signal received from laser beam output detection means in response to a control signal for controlling a deflection angle adjustment unit of the deflection unit. Then, the control unit arithmetically operates the ratio of an actual output power corresponding to the control signal with reference to the lowest value of the actual output power. Further, the control unit arithmetically operates a correction value corresponding to the ratio of the actual output power to produce a control map and controls the output adjustment unit based on the control map.