A needle assembly for transdermal administration including a substrate having a first surface and a second surface opposite to the first surface, and fine needles projecting perpendicularly from the first surface. The substrate has grooves on at least one of the first surface and the second surface, and the grooves are formed such that the substrate is deformable following a surface shape of a skin to allow axes of the fine needles to extend in a direction normal to the surface of the skin.
