An endoscopic aspiration device is mounted on a manipulating head of an endoscope, from which an elongated insertion rod member is extended forward, the endoscopic aspiration device being composed of a valve casing which is mounted on the manipulation head in communication with an aspiration passage running through the insertion rod member, and a valve assembly unit including a valve member, a valve guide member and a connector member attached to the valve guide member to communicate same with a proximal aspiration passage on the side of a suction source. The valve member is put in a sliding displacement along the valve guide member to bring the aspiration passage into and out of communication with the proximal aspiration passage on the side of a suction source. The valve guide member is coupled with the valve casing through a coupling mechanism which permits to turn the valve assembly unit on and relative to the manipulating head. The coupling mechanism is arranged to perform a function of coupling and uncoupling the valve guide unit with and from the valve casing, and a function of locking the valve guide member in the valve casing to prevent spontaneous dislodgement from the latter.