To provide a plant stem-smoothing tool and a method for smoothing plant stems, which are each simplified, make it possible to firmly bind stems exerting no burden on the plant stems, and to easily and simply carry out work to change the binding positions of the stems.

This plant stem-training tool is used for training plant stems, and comprises a rope for hanging the stems down from above, a ring body having a diameter of twice or more of a rope diameter, and a fastening string for tying up the plant stems; wherein part of the rope is formed in a U-shape so as to be put through the hollow part of the ring, and the fastening string is put through the inside of the U-shaped rope put through the hollow part.