<p>A medical instrument (1) has a first unit (A) and a second unit (B). The first unit (A) has a vertically elongate body (2), a guide section (slide section (23)) projecting from the lower end of the body in the direction that intersects the vertical direction and having formed in it first and second guide holes (235, 236), a hollow structured first puncture needle (4) supported near its upper end by the body so as to be slidable in the vertical direction and having a sharp lower end slidably inserted in a first guide hole from above, and a first holding plate (61) integrally fixed to the vicinity of the upper end of the first puncture needle (4). The second unit (B) has a second puncture needle (3) inserted in a second guide hole and also has a second holding plate (62) integrally fixed near the upper end of the second puncture needle. The second holding plate makes contact from above with the first holding plate in a contactable and separable manner. The position of the second hole is selectable along the length of the guide section.</p>
