An infusion set employing a spike cap, arranged at which there is an opening configured to prevent passage therethrough of solid or liquid but to allow passage therethrough of gas at interior of the cap, hydrophobic filter being arranged at a location inward from where a tip of spike is inserted at interior of the cap by way of an insertion port, and a lid exterior of the opening for closing the opening; and in which there are hook(s) for anchoring to infusion tubing and a clip equipped with a catch for a flange arranged at the spike. Employing the cap at the infusion set makes it possible to carry out preprocessing including priming and backpriming by a simple operation without leakage of liquid.