A puncture device used with a puncture needle unit attached to the device. The puncture needle unit has a puncture needle and a tubular casing. The puncture needle has a needle body having a sharp needle point at the tip of the needle body and also has a needle hub fixed to the base of the needle body. The tubular casing houses the puncture needle so that the puncture needle can move along the longitudinal direction of the puncture needle, and the tubular casing has an opening from which the needle point can protrude. The puncture device has a hollow housing, a ring-like mounting section provided to the head of the housing and to the inner side of which the casing is removably mounted, and a plunger housed in the housing and having a tubular connection section connecting to the needle hub in a mounted state in which the casing is mounted to the mounting section. The connection section has ribs circumferentially arranged on the outer peripheral surface of the connection section so as to extend along the center axis of the connection section. In the mounted state, the connection section and the needle hub are connected to each other and a gap is formed between the outer peripheral surface of the connection section and the inner peripheral surface of the casing with the ribs located in the gap.
