An injection instrument is provided to reliably administer a medicine into the skin while inhibiting leakage of the medicine to the surface of the skin. An injection instrument according to an aspect of the present invention includes: a hollow needle body (10) including one or more projections (12) on a first surface (11S) of a substrate (11), each projection (12) being formed with a through hole a deforming part (25) arranged on an outer peripheral side of the one or more projections (12), the deforming part (25) being deformable in a direction bulging from the first surface (11S) and a pressure channel (26) that applies a fluid pressure to the deforming part (25), wherein the deforming part (25) is deformable in a projecting direction of the projections (12) from the first surface (11S) in response to the fluid pressure.
