A ball joint, which rotatably and vibratably connects two portions which can move relative in a suspension mechanism of a vehicle, comprising: a ball stud having a columnar stud portion and a ball portion which has a spherical side surface and a center positioned on an axis of the stud portion; a ball seat which is made of a resin and has a spherical recess portion into which the ball portion is relatively rotatably and slidably fitted; a housing which is made of a resin and holds the ball seat therein; and a support bar which is connected with the housing, wherein the housing has a boss portion having an opening portion which opens at a side surface of the housing, the support bar has a bar portion and a flange portion, the bar portion being a center portion extending along an axis of the support bar, the flange portion formed at a leading end portion of the bar portion, the housing is formed by injection using the resin so that the boss portion of the housing directly covers a leading end portion of the support bar which includes the flange portion, and the support bar is connected with the boss portion so that the opening portion is formed in close contact with and covers an entire periphery of the flange portion, and the support bar has plural protruding portions at the flange portion side of the bar portion, the opening portion is formed in close contact with and covers entire peripheries of the protruding portions. a ball stud having a columnar stud portion and a ball portion which has a spherical side surface and a center positioned on an axis of the stud portion; a ball seat which is made of a resin and has a spherical recess portion into which the ball portion is relatively rotatably and slidably fitted; a housing which is made of a resin and holds the ball seat therein; and a support bar which is connected with the housing, wherein the housing has a boss portion having an opening portion which opens at a side surface of the housing, the support bar has a bar portion and a flange portion, the bar portion being a center portion extending along an axis of the support bar, the flange portion formed at a leading end portion of the bar portion, the housing is formed by injection using the resin so that the boss portion of the housing directly covers a leading end portion of the support bar which includes the flange portion, and the support bar is connected with the boss portion so that the opening portion is formed in close contact with and covers an entire periphery of the flange portion, and the support bar has plural protruding portions at the flange portion side of the bar portion, the opening portion is formed in close contact with and covers entire peripheries of the protruding portions. the support bar has a bar portion and a flange portion, the bar portion being a center portion extending along an axis of the support bar, the flange portion formed at a leading end portion of the bar portion, the housing is formed by injection using the resin so that the boss portion of the housing directly covers a leading end portion of the support bar which includes the flange portion, and the support bar is connected with the boss portion so that the opening portion is formed in close contact with and covers an entire periphery of the flange portion, and the support bar has plural protruding portions at the flange portion side of the bar portion, the opening portion is formed in close contact with and covers entire peripheries of the protruding portions.