This syringe assembly 10 is provided with: a barrel 2 with a puncture needle； and a cap 3 which is mounted on the barrel 2 and into which the tip 61 of the puncture needle 6 is inserted. The cap 3 comprises: a seal cap comprising an elastic material and including water vapor permeable properties for autoclave sterilization； and a cylindrical cover member 8 comprising a thermoplastic plastic material which is harder than the seal cap 7. The cap 3 is configured so that by autoclave sterilization, the force of engagement between the cylindrical cover member 8 and the seal cap 7 is increased compared to before sterilization.
