A laser irradiation apparatus comprising: a long and slender main body 101; an optical fiber 107, which is placed inside the main body 101 and which is equipped with a proximal end through which a laser ray is introduced and an emitting part from which the laser ray is emitted sideways or diagonally; and a reflecting member 151, which is affixed inside said main body 101 and reflects laser ray emitted from the optical fiber 107. The emitting part of the optical fiber 107 is capable of making a reciprocating motion in the lengthwise direction inside the main body 101 within the specified range. The reflecting member 151 has a reflecting surface 152 that changes its reflecting angle as the emitting part of the optical fiber 107 moves along its reciprocating movement range.