To provide a retaining pin that is easily attachable and detachable without using a tool and does not carelessly fall out from the set position.

The retaining pin 1 is inserted into a tip hole 5 at the tip of a connecting shaft 2 and prevents the same from slipping off, the connecting shaft 2 being inserted into shaft-insertion holes 17 of at least two members to be connected as the shaft-insertion holes 17 remain communicating with each other. The retaining pin 1 is made of an elastic metal and composed of an insertion shaft 3 of straight-line form to be inserted into the tip hole 5 and a ring part 7 connected to one end of the insertion shaft 3 and extending toward the other end of the insertion shaft 3, wherein the insertion shaft 3 is located on the line passing near the center of the ring part 7 and the other end of the insertion shaft 3 protrudes from the ring part 7.