A blocking device for blocking a semi-finished optical element having a first face to which the blocking device is to be attached and having opposite to the first face a second face to be surfaced in a surfacing machine configured for holding the semi-finished optical element via the blocking device, said blocking device comprising: - a mounting portion provided for mounting the blocking device on a corresponding mounting member of said surfacing machine; and - a blocking portion configured for blocking said semi-finished optical element; said blocking portion comprising a support member configured for providing a rigid support to said semi-finished optical element, said support member including a support element made of a shape-memory material having a rigid state below a predetermined temperature and a plastic state above said predetermined temperature, said support element assuming in the absence of external forces a predetermined memory shape when heated above said predetermined temperature, said support member having a contact face onto which said first face of said semi-finished optical element is to be applied; characterized in that the support element is made of a single piece, said contact face of said support member is a surface of said support element and said shape-memory material is configured for having adherence properties with respect to said first face of said semi-finished optical element when said contact face of said support element and said first face of said semi-finished optical element are in direct contact with each other, said adherence properties being sufficient for attaching said first face of said semi-finished optical element to said contact face of said support element so that the semi-finished optical element can be surfaced in the surfacing machine. - a mounting portion provided for mounting the blocking device on a corresponding mounting member of said surfacing machine; and - a blocking portion configured for blocking said semi-finished optical element; said blocking portion comprising a support member configured for providing a rigid support to said semi-finished optical element, said support member including a support element made of a shape-memory material having a rigid state below a predetermined temperature and a plastic state above said predetermined temperature, said support element assuming in the absence of external forces a predetermined memory shape when heated above said predetermined temperature, said support member having a contact face onto which said first face of said semi-finished optical element is to be applied; characterized in that the support element is made of a single piece, said contact face of said support member is a surface of said support element and said shape-memory material is configured for having adherence properties with respect to said first face of said semi-finished optical element when said contact face of said support element and said first face of said semi-finished optical element are in direct contact with each other, said adherence properties being sufficient for attaching said first face of said semi-finished optical element to said contact face of said support element so that the semi-finished optical element can be surfaced in the surfacing machine.