Abstract: The present invention discloses a of drainage device comprising a drainage device main body, a filter, a seal member and a fixing member, characterized in that, several protrusions are provided in equal interval around an outer circumferential surface of the drainage device main body. The fixing member is a circular ring that corresponds in shape with the drainage device main body. An annular groove is provided along a circumference of a back side of the circular ring. Notches in number corresponding to that of the protrusions are provided in equal interval around an inner circumferential surface of the circular ring. Several locking slots each in shape of an arc and continuously arranged one by one in the same direction are provided around the inner circumferential surface of the circular ring along each of the notches. Several self-locking pins are also provided on the circular ring.