To make it possible to prevent the excessive pressure of a catheter by injecting a working material for removing clogging into the catheter and releasing the excessive pressure in the catheter.

A hub 60 generally connected to a liquid supplying source is used for receiving a clot removing agent for removing the clogging in the catheter 50. This hub 62 is provided with an excessive pressure releasing valve 64, which releases the excessive pressure by opening at the time of introducing the clot removing agent into the cannula of the catheter 50. Namely, the hub 62 is disconnected from the liquid supplying source and is connected to a clot removing agent supplying source to open the excessive pressure releasing valve 64 in the case the clogging is removed. The clot removing agent is supplied and the excessive pressure is released. As a result, the excessive pressure state generated by the injection of the clot removing agent is prevented and the safety is assured.