b having at its connection end a connecting means 49 of which shape corresponds to that of the connecting means 44 of fig9 a that is the catheter and the infusion line 47 can be airtightly and securely connected to each other by sticking a needle 50 of the infusion line 47 into a rubber plug 41 of the injection site 43 of the catheter to make the catheter communicate with the infusion line 47 and then by combining both connecting means the injection site 43 is used for infusing plural kinds of liquid drug into a patient by adding other liquid drugs from other infusion lines during fluid therapy the injection site 43 comprises a tubular body having one or more fluid inlet and a fluid outlet a cap or plug made of rubber like elastic material is liquidtightly put on at least one fluid inlet in the case of a cap it is put on the fluid inlet while in the case of a plug it is inserted into the fluid inlet as shown in fig9 a in that case a means for supporting the cap or rubber plug 41 might be provided to prevent the detachment of the cap or rubber plug 41 in fig9 a the connecting means 44 functions also as a supporting means as a material for the cap or plug the same material as in the cap or plug of the above mentioned connector can be employed the connecting means 44 serves to connect a catheter to a device to be connected hereafter representatively referred to as infusion line and the device has a needle at its connection.