A swing clamp apparatus is provided in which the clamp arm is positioned and attached to a clamp rod at a desired position in a simple and reliable manner and the clamp arm replacement workload is certainly reduced. The swing clamp apparatus comprises an attachment block fixed to the leading end of a clamp rod and to which a clamp arm is detachably attached and a pair of clamping force transmission pins inserted in the attachment block and clamp arm in the direction parallel to the orthogonal direction to the axis for coupling the positioned clamp arm to the attachment block in an integrated manner.