PURPOSE: To increase the interval between a spring member and a frame member by a spherical projection and a support member and to attach and detach an original pressure plate smoothly by providing the spherical projection to the spring member.

CONSTITUTION: When the original pressure plate 1 is inserted from above as shown by an arrow A so that the plate 1 is set on the frame member 4, the tips of support member 2 abut on the spherical projections of spring member 5 and when the original pressure plate 1 is further inserted, forces operate on the spherical projections of the spring members 4 in leaving directions from the frame member 4, so that the support members 2 are further inserted. At this time, the support members 2 receive reaction forces from the spring member 5 and are pressed against the frame member 4 and fixed tightly. When the original pressure plate is detached, it is detached smoothly by the same operation with the insertion. Consequently, the attachment and detachment are performed smoothly.