A clamp apparatus is equipped with a cylinder mechanism having a piston. A driving force of the cylinder mechanism is transmitted to a clamp arm, which is retained on a housing through a block body and a link pin that make up a driving force transmitting mechanism, the clamp arm being rotated through a predetermined angle. The block body includes a rotatably supported roller. The block body is guided along an axial direction by displacement of the roller, while the roller is rotated along a guide member of the housing.