On a rigid tip end section at the distal end of an elongated endoscopic insertion member, an observation window washer means is provided to wash an endoscopic optical observation window, along with a fluid injection means to be used for injecting a fluid from an injection passage leading to an injection hole opened on the rigid tip end section of the insertion member. Connection ports to a wash liquid conduit and a compressed air conduit of the observation window washer means are opened at a conduit connection terminal of a multiplex connector on a proximal end of a universal connection cable. Disconnectibly connected to the conduit connection terminal is a conduit coupler member having a wash liquid conduit and a compressed air conduit to supply a wash liquid and compressed air to the wash liquid conduit and compressed air conduit on the side of the conduit connection terminal. Further, an end of a injection passage is opened in the conduit connection terminal, while an injection fluid feed line is disconnectibly connected to a connection port which is provided at a lateral side of the conduit coupler member and which is brought into communication with the injection passage when the conduit coupler member is plugged into the conduit connection terminal.
