Abstract: Provided is a ball joint which enhances a sealing performance between a boot seal (4) and a ball shank (1) and which can maintain this sealing performance even during swinging motion of the ball shank (1) with respect to a holder (2), making it possible to completely prevent intrusion of dust and muddy water into a ball reception portion (20) of the holder (2) The ball shank (1) is provided with a flange portion (13), with a tapered surface (16) inclined with respect to an axial direction of the ball shank (1) being formed on the flange portion (13). The boot seal (4) is constructed of an annular fixation portion fixed to the holder (2), an annular seal portion (42) tightening a shaft portion (10) of the ball shank (1) and held in press contact with the flange portion (13).