Provided are a medical needle and a puncturing instrument which make it possible to administer a predetermined amount of a substance to be administered into a living body and/or collect a predetermined amount of an object to be collected from within the living body with ease and accuracy. A medical needle (1) is provided with a puncturing part (10) which can penetrate into the living body. The puncturing part (10) has a pair of planar portions (12, 12) which are parallel to each other in an outer surface and a retaining chamber (18) defined within the puncturing part (10), the retaining chamber (18) passing through the puncturing part (10) and opening to the pair of planar portions (12) on each side. A puncturing instrument can be structured by accommodating the medical needle (1) in a casing in such a way that the medical needle (1) can project therefrom.