A clamp apparatus includes a pair of first and second clamp arms. A driving force transmission mechanism transmits a driving force of a drive unit, whereby the first clamp arm is operated to rotate via a link arm, while simultaneously, the second clamp arm is rotated, and after being rotated through a predetermined angle, under moving action of a roller, which is inserted into a cam groove of a link plate, rotation of the second clamp arm is stopped and maintained in advance with respect to the first clamp arm. Consequently, after positioning of a workpiece has been carried out by the second clamp arm, rotation of which is stopped, the first clamp arm continues to be rotated, whereby the workpiece is clamped.