To provide a synthetic resin ball seat capable of maintaining its uniform sliding torque and preventing its rattling by preventing the degradation of load resistance and durability and still preventing the deformation of a spherical band-shaped portion on the opening side through which a ball stud passes, and to provide a ball joint using the same.

The ball joint 1 includes a socket 4 having a cylindrical inner face 2 and a spherical band-shaped inner face 3, the synthetic resin ball seat 7 having a cylindrical outer face 5 contacting the cylindrical inner face 2 of the socket 4 and a spherical band-shaped outer face 6, and the ball stud 13 including a ball part 12 having a spherical outer face 11 contacting each of spherical band-shaped faces 8, 10 of the ball seat 7, and disposed in the socket 4.