A device for connecting a catheter to an injection tube, which is provided with an elastic tube into which an open end of the tubular catheter having electrodes disposed at the closed end thereof and also having conductive wires connected to said electrodes and taken out at the open end thereof and an open end of the injection tube having a mechanism for fluid injection at the other end thereof are inserted so that both open ends are connected end-to-end and the conductive wires are taken out through a gap between the elastic tube and the injection tube; and a sealing agent to cover respective surfaces of the catheter, injection tube, and elastic tube which surfaces are coated with an adhesive. The catheter, injection tube, and elastic tube, when coated with an adhesive of high viscosity, are compatible with the hard sealing agent lying thereabove. A casing consisting of half members encloses the sealing agent and the casing increases the strength of the device, whereby the device is prevented from being deformed and prevented from causing leakage of fluid through the gap even when subjected to external force. The device has improved resistance to external pressure. In addition, connection of the conductive wires between the electrodes and the terminals arranged on the side of the casing serves to tightly fix the wires in the sealing agent packed in the case and causes no breakage of the wires, whereby the wires are connected to the external parts through the terminals to thereby provide a device with improved reliability.