To realize a wafer holding mechanism which are capable of surely performing a clamping/unclamping action, dispensing with an installation space, making the pinching pawls function surely synchronize with each other, easily regulating a clamping pressure, and generating less dust by a method wherein the pinching pawls are moved by the action of a multi-apex cam at the same time.

A pentagonal cam 2 which is possessed of apexes on its outer circumference and recesses each located between the two adjacent apexes and capable of pivoting to a base 5, an energizing means which energizes a movable pawl toward a wafer pinching side making it bear against the outer circumference of the pentagonal cam 2, a swing arm 7 which rotates the pentagonal cam 2 in one direction and rotates reversely in the opposite direction for recovering so as to move the bearing point of the pentagonal cam 2 which the movable pawl bears against between the apex and recess, and a pull-push wire 1 are provided. The movement of the cable core of the pull-push wire 1 in the lengthwise direction is changed to the movement of the swing arm 7, then the movement of the swing arm is changed to the rotary motion of the pentagonal cam 2, and then the rotary motion of the pentagonal cam 2 is changed to the rectilinear movement of the pinching pawls for chucking or unchucking a wafer.