To provide an eccentric adaptor for straight pipe with high quality and satisfactory maintainability which satisfies the standard for certifying fine housing parts or the like declared by an organization for evaluating residential performance designated by the quality assurance standard for a residential drain pipe.

This adaptor comprises a body having a circular opening part on the upper surface; a connection part with a building-side drain port or the upper end of a straight pipe, which is integrally provided on the lower part of the body eccentrically from the central axis of the opening part; a rotating part rotatably mounted on the opening part; and a connection part with the lower end of the straight pipe or an equipment-side drain port, which is integrally provided on the rotating plate eccentrically from the central axis thereof. Accordingly, even if the equipment-side drain port is axially shifted from the building-side drain port, this slippage can be absorbed to connect the both through the straight pipe. The bottom surface of the body is inclined downward, and the rotating part is adhered to the opening part of the body after positioning the connection parts.