A puncture needle includes: a puncture portion including: a distal part including a blade surface, and a proximal part having a substantially constant outer diameter; and a retained portion connected to the proximal part of the puncture portion and configured to be retained by a hub. The retained portion includes: a tubular portion having a substantially constant outer diameter larger than a maximum outer diameter of the proximal part of the puncture portion, and a tapered portion located between the proximal part of the puncture portion and the tubular portion. The puncture portion includes a slit. In the tapered portion, in a top view with the slit facing upward, an outermost diameter of the puncture needle gradually increases from a puncture portion side to a tubular portion side, while a width of the slit gradually decreases from the puncture portion side to the tubular portion side.