To provide a dialyzing coupler capable of reconciling both of the keeping of an excellent aseptic state and excellent operability at the time of attachment and detachment to a nozzle.

The dialyzing coupler includes the sleeve having the seal material applied to a dialyzing solution circulating nozzle arranged to the inner periphery thereof and fixed to the outer periphery of the seal material, the spring material coming into contact with the sleeve and capable of extending and contracting in the direction sealed to the nozzle and the slider sliding along the sleeve by the extension and contraction of the spring material. A ring-shaped member is provided between the seal material and the slider and pressed by the sliding of the slider to increase the liquid tightness between the seal material and the leading end part of the nozzle at the time of sealing.