To perform easy and reliable confirmation of flare processing for connection to a mating member and connection and to prevent the damage of reliability.

In such a state that the bellows shape part 21 of a protector 20 is contracted and the tip of a resin tube 10 is exposed, the resin tube is inserted externally of the nip 31 of a connector 30 for fit-in. Since the tip of a resin tube forms a flare part 11 in the shape of a funnel, a resin tube is fitted in a connector without damaging an O-ring 33. It is confirmed by a sensor that the two members are reliably fitted in each other. Thereafter, by restoring the shape of a contracted bellows part, the tip of an exposed resin tube is covered with the bellows shape part. As a result, the whole of the resin tube containing a connection part is protected by a protector, whereby reliability of the resin tune is ensured.