A tapered optical needle includes a tapered light-transmissive needle and a surface plasmon wave transport layer. The tapered light-transmissive needle has a first tip, a bottom, and a curved surface connecting the first tip and the bottom. The surface plasmon wave transport layer is disposed on the curved surface and covers the first tip, wherein the surface plasmon wave transport layer has a curved slit structure. The curved slit structure includes a plurality of curved portions arranged from the first tip to an edge of the bottom and located between the first tip and the edge of the bottom, and extending directions of the curved portions are different to a direction from the first tip to the edge of the bottom.