Abstract: A swashplate type hydraulic device has a ball joint which includes a spherical socket of a major arc longitudinal section formed in a plunger or a shoe member and a ball formed at an end of a connecting rod which connects the plunger and the shoe member, the ball being fitted in the socket so as to permit a swing motion of the rod around the ball, the inlet of the socket having a center offset by a predetermined amount of distance from the center of the socket while the ball having a cylindrical portion which can be fitted in the inlet and which has a center located offset from the center of the ball by an amount equal to the offset amount of the inlet center relative to the socket center, the centers of the inlet and the cylindrical portion being offset relative to each other in a fitted state of the socket and ball. The ball includes a chamferred portion to permit the ball to be fitted in the socket when the rod is at a position outside its normal swinging range.