Positioning and blocking device for positioning and blocking a piece (P) with respect to a working table (WT), comprising: - a body comprises a head , - blocking means for blocking said piece (P), arranged on said head and configured to assume a first condition, where said blocking means does not block said piece (P), and a second condition, where said blocking means block said piece (P), - a first opening provided in said body and configured to be connected, when the positioning and blocking device is in use, to a depression generating device (D) for generating a depression, - a second opening arranged on said head , - a first duct extending between said first opening and said second opening , - an abutment element , movable between a rest position and an operational position, wherein said positioning and blocking device comprises a second duct , connected to said abutment element , and said positioning and blocking device is configured in such a way that, when said depression generating device (D) generates a depression in said first duct through said first opening , said blocking means assume said second condition and said abutment element moves from the operational position to the rest position, characterized in that said second duct connects said abutment element to said first duct in such a way that, when said blocking means assume said second condition, said second duct is in communication with said first duct , in that said positioning and blocking device is provided with a check valve , arranged on said head at said second opening , to prevent or allow the passage of a fluid from said first duct to said second duct and/or from said first duct to the external environment. - a body comprises a head , - blocking means for blocking said piece (P), arranged on said head and configured to assume a first condition, where said blocking means does not block said piece (P), and a second condition, where said blocking means block said piece (P), - a first opening provided in said body and configured to be connected, when the positioning and blocking device is in use, to a depression generating device (D) for generating a depression, - a second opening arranged on said head , - a first duct extending between said first opening and said second opening , - an abutment element , movable between a rest position and an operational position, wherein said positioning and blocking device comprises a second duct , connected to said abutment element , and said positioning and blocking device is configured in such a way that, when said depression generating device (D) generates a depression in said first duct through said first opening , said blocking means assume said second condition and said abutment element moves from the operational position to the rest position, characterized in that said second duct connects said abutment element to said first duct in such a way that, when said blocking means assume said second condition, said second duct is in communication with said first duct , in that said positioning and blocking device is provided with a check valve , arranged on said head at said second opening , to prevent or allow the passage of a fluid from said first duct to said second duct and/or from said first duct to the external environment. <EOS>