To provide a ball joint structure of a windshield wiper with capability to make progress in abrasion of a whole contact surface of a ball retainer uniform to improve endurance of the ball joint.

The ball joint structure of the windshield wipe has ball pins 11 fixed to a crank arm 3 fixed to an output shaft of a wiper motor and a pivot arm 13 fixed to a pivot shaft for making a wiper arm swing, respectively. The ball retainer 12 fitted to a link connecting rod 6 for connecting the crank arm 3 and the pivot arm is, in its own spherical contrapositins, fitted into a spherical portion 11a of each ball pin 11 in a freely sliding manner. Sliding surfaces 12f of the ball retainer 12 sliding on a spherical surface 11b of the spherical portion 11a of the ball pins 11 are formed in a vertically symmetrical manner defining a horizontal center line S passing through the center C of the spherical portion 11a as a reference.