A constant-velocity joint assembly includes: a first and a second shaft portions respectively provided with a protrusion; a double yoke portion in which a guide hole is formed along an axis direction, the first and the second shaft portions being respectively rotatably connected to both sides of the guide hole with an axis of an upper/lower direction; and a guide portion which is disposed to the guide hole to guide the protrusion and rotates along an inner circumference of the guide hole during rotation of the shaft portions, wherein the first and the second shaft portions respectively comprises: a spider body, a left and a right leg, and an upper and a lower legs; a shaft provided with the protrusion; and a yoke block comprising a block body, and a left and a right connecting member.