An injection instrument including a hollow needle body including a substrate having a first surface and a second surface opposite to the first surface, the hollow needle body having at least one projection which is formed on the first surface and has a through hole penetrating from a distal end of the projection to the second surface of the substrate, a deforming member positioned outside a region where the at least one projection is formed, the deforming member being deformable to bulge in a bulging direction along a projecting direction of the projection beyond a plane flush with the first surface, and a pressure channel through which a fluid is supplied such that a fluid pressure is applied to the deforming member. The deforming member is deformable in the bulging direction in response to the fluid pressure.
