A workpiece gripping device for machine tools and machining centers, comprising a body, grip means (32, 34), which can move with respect to the body between a loading/unloading position and a gripping position, elastic means arranged to bias said grip means (32, 34) towards said gripping position, pneumatic actuation means, which can be activated to actuate selectively said grip means (32, 34) either toward said gripping position in aid of said elastic means, or toward said loading/unloading position in contrast with said elastic means, by means of a first circuit and a second circuit respectively, wherein said first circuit and said second circuit are configured to be selectively supplied with pressurized air, characterized in that it comprises valve means provided with a first port and with a second port, which can be connected selectively and temporarily to a pressurized air source and are connected respectively to said first circuit and to said second circuit via flow control means (58, 80, 82) wherein said flow control means (58, 80, 82) are movable as a consequence of the air pressure supplied through said first port or said second port, so as to connect said first port to said first circuit and said second port to said second circuit, when said pressurized air source is connected to said first port and said second port is put to discharge, seal said first circuit when it is pressurized and the pressurized air source is disconnected from said first port, so as to maintain said grip means (32, 34) in said gripping position when disconnected from said pressurized air source, connect said second port to said second circuit and said first port to said first circuit, when the pressurized air source is connected to said second port and said first port is put to discharge, seal said second circuit when it is pressurized and the pressurized air source is disconnected from said second portion so as to maintain said grip means (32, 34) in said loading/unloading position when disconnected from said pressurized air source. a body, grip means (32, 34), which can move with respect to the body between a loading/unloading position and a gripping position, elastic means arranged to bias said grip means (32, 34) towards said gripping position, pneumatic actuation means, which can be activated to actuate selectively said grip means (32, 34) either toward said gripping position in aid of said elastic means, or toward said loading/unloading position in contrast with said elastic means, by means of a first circuit and a second circuit respectively, wherein said first circuit and said second circuit are configured to be selectively supplied with pressurized air, characterized in that it comprises valve means provided with a first port and with a second port, which can be connected selectively and temporarily to a pressurized air source and are connected respectively to said first circuit and to said second circuit via flow control means (58, 80, 82) wherein said flow control means (58, 80, 82) are movable as a consequence of the air pressure supplied through said first port or said second port, so as to connect said first port to said first circuit and said second port to said second circuit, when said pressurized air source is connected to said first port and said second port is put to discharge, seal said first circuit when it is pressurized and the pressurized air source is disconnected from said first port, so as to maintain said grip means (32, 34) in said gripping position when disconnected from said pressurized air source, connect said second port to said second circuit and said first port to said first circuit, when the pressurized air source is connected to said second port and said first port is put to discharge, seal said second circuit when it is pressurized and the pressurized air source is disconnected from said second portion so as to maintain said grip means (32, 34) in said loading/unloading position when disconnected from said pressurized air source.