A coupling joint includes: joint member which has gear teeth; a center tube which has gear teeth meshing with the gear teeth, and through which a rotational force is transmitted between the joint member via the gear teeth and the gear teeth; a seal member which blocks a lubricated space including a meshing portion of the gear teeth and the gear teeth from the outside between the joint member and the center tube; a lubricant which fills the lubricated space; and a pressure-equalizing member which is provided to face a part of the lubricated space, changes the volume of the lubricated space by deforming in accordance with the pressure of the outside, and thereby equalizes the pressure of the lubricant and the pressure of the outside.