To enable even frictional contact of a frictional surface body by forming a frictional surface to substantially be an outer surface of a spherical base, and locating a center of the spherical base at an axis of a circular frictional member, and outside a bottom plane of the spherical base.

A frictional surface 4 is formed on a free inner surface of a friction lining 3, and formed to be an outer surface of substantially a spherical base, not true truncated cone formed between a support surface 6 and a holding ring 2. A center point M of the spherical base is located at an intersection of an axis 5 of a frictional member 1 and a vertical line R in respect to a conical angle Y selected for torque transmission. The vertical line R is located at a half position of frictional width (Z/2). The center M of the spherical base is located at a passing point of the axis 5 passing a bottom plane of the spherical base due to relation between the width of the frictional member and the conical angle Y. The bottom plane of the spherical base is agreed with an upper limit of the frictional member 1.