A puncture needle for ultrasound biopsy used in combination with an ultrasonic endoscope (1,1') including a distal-end hard part (2a, 2a'), a bendable part which is connected to a proximal end of the distal-end hard part (2a, 2a') and which is bendable, and an operation part which performs bending operation of the bendable part, the puncture needle comprising: a sheath that is inserted into an insertion channel of the ultrasonic endoscope (1, 1') so as to be capable of advancing and retracting; a needle tube that has a predetermined outer diameter so as to be inserted into the sheath, and a sharp distal end configured to puncture a tissue in a body cavity; and a releasing mechanism that is fitted to a proximal-end side of the needle tube, and releases a substance (35, 53) filled therein from an opening of the needle tube to an outside, characterized in that the needle tube has an inner cavity which extends along a longitudinal axis of the needle tube and which centers on a position displaced from a center of the outer diameter, a thinnest part in which a thickness of a border of the opening, which is formed in a distal-end region of the needle tube so as to communicate with the inner cavity, is the thinnest, and a thickest part in which the thickness is the thickest, a direction of the opening of the needle tube is substantially parallel with a cross-sectional plane connecting the thinnest part and the thickest part, in a state in which the needle tube is disposed inside the bendable part, a periphery of the needle tube receives a force from an inner wall of the insertion channel while the bendable part is in a bent state by the operation part, and the needle tube is rotated around a longitudinal axis of the insertion channel by the force, such that the thinnest part is disposed on an inside of the bendable part and an axis line matching the direction of the opening in the needle tube protruding from the insertion channel becomes substantially parallel with an ultrasonic scanning face (10A, 10A') of the ultrasonic endoscope (1, 1'). a sheath that is inserted into an insertion channel of the ultrasonic endoscope (1, 1') so as to be capable of advancing and retracting; a needle tube that has a predetermined outer diameter so as to be inserted into the sheath, and a sharp distal end configured to puncture a tissue in a body cavity; and a releasing mechanism that is fitted to a proximal-end side of the needle tube, and releases a substance (35, 53) filled therein from an opening of the needle tube to an outside, characterized in that the needle tube has an inner cavity which extends along a longitudinal axis of the needle tube and which centers on a position displaced from a center of the outer diameter, a thinnest part in which a thickness of a border of the opening, which is formed in a distal-end region of the needle tube so as to communicate with the inner cavity, is the thinnest, and a thickest part in which the thickness is the thickest, a direction of the opening of the needle tube is substantially parallel with a cross-sectional plane connecting the thinnest part and the thickest part, in a state in which the needle tube is disposed inside the bendable part, a periphery of the needle tube receives a force from an inner wall of the insertion channel while the bendable part is in a bent state by the operation part, and the needle tube is rotated around a longitudinal axis of the insertion channel by the force, such that the thinnest part is disposed on an inside of the bendable part and an axis line matching the direction of the opening in the needle tube protruding from the insertion channel becomes substantially parallel with an ultrasonic scanning face (10A, 10A') of the ultrasonic endoscope (1, 1').