A constant velocity joint for a drive system comprises: an outer race having a plurality of guide grooves formed in an axial direction in the inner spherical surface of the outer race; an inner race having a plurality of guide grooves formed in an axial direction in the outer spherical surface of the inner race, said guide grooves of the outer race and the inner race together forming a plurality of ball guide tracks; a plurality of balls disposed in the ball guide tracks; and a cage installed between the inner spherical surface of the outer race and the outer spherical surface of the inner race, said cage having a plurality of windows for retaining the balls therein. Each guide groove of the outer race is shaped to have a longitudinal cross section formed with two circular regions with different centers, a first circular region disposed at a first lateral side of the outer race and a second circular region disposed at a second lateral side of the outer race, and a linear region tangentially extending between these two circular regions, and each guide groove of the inner race is shaped to have a longitudinal cross section formed with two circular regions with different centers, a first circular region disposed at a first lateral side of the inner race and a second circular region disposed at a second lateral side of the inner race, and a linear region tangentially extending between these two circular regions.