A dispensing device (1; 101; 201) for a liquid or paste-like dispensable comprising: - a connecting member (10; 110; 210) to be placed at the end of the open end of a container holding the product to be dispensed, - a piston (3; 103; 203) fixedly arranged with respect to the connecting member (10;110;210), - a cylinder body (6; 106; 206) in which the piston (3; 103; 203) is arranged so as to define a metering chamber (100; 200; 300) between the piston (3; 103; 203) and the cylinder body (6; 106; 206), the piston (3; 103; 203) comprising at least one upstream opening forming an inlet of the metering chamber (100; 200; 300), the so-called metering inlet (35; 135; 235), and the metering chamber (100; 200; 300) comprising an outlet, the so-called metering outlet (73; 173; 273), the cylinder body (6; 106; 206) being slidably movable along the piston (3; 103; 203) between an extended position and a retracted position, the dispensing device also includes an inlet check valve (5; 105) mounted on the piston (3; 103; 203) and comprising an inlet diaphragm having a concave shape, the piston (3; 103; 203) comprises a first part (30; 130; 230); and a second part forming a seal (40; 140; 240) which is fitted or overmoulded around at least a portion of the first part (30; 130; 230), said seal (40; 140; 240) is made of a flexible material compared to the first part (30; 130; 230) of the piston (3; 103; 203) made of a rigid material, said seal (40; 140; 240) reinforcing the seal between the piston (3; 103; 203) and the side wall(s) of the cylinder body (6; 106; 206), the piston (3; 103; 203) and the inlet check valve (5; 105) forming separate piece and being arranged so as: - that, when the cylinder body (6; 106; 206) is stationary or moves to the retracted position, the inlet diaphragm is in a tight clamping position with the top of said seal (40; 140; 240) and closes the metering inlet (35; 135; 235), and - that the concave shape of the inlet diaphragm deforms elastically and opens the metering inlet (35; 135; 235) when subjected to a negative pressure generated in the metering chamber (100; 200; 300) upon displacement of the cylinder body (6; 106; 206) to its extended position. - a connecting member (10; 110; 210) to be placed at the end of the open end of a container holding the product to be dispensed, - a piston (3; 103; 203) fixedly arranged with respect to the connecting member (10;110;210), - a cylinder body (6; 106; 206) in which the piston (3; 103; 203) is arranged so as to define a metering chamber (100; 200; 300) between the piston (3; 103; 203) and the cylinder body (6; 106; 206), the piston (3; 103; 203) comprising at least one upstream opening forming an inlet of the metering chamber (100; 200; 300), the so-called metering inlet (35; 135; 235), and the metering chamber (100; 200; 300) comprising an outlet, the so-called metering outlet (73; 173; 273), the cylinder body (6; 106; 206) being slidably movable along the piston (3; 103; 203) between an extended position and a retracted position, the dispensing device also includes an inlet check valve (5; 105) mounted on the piston (3; 103; 203) and comprising an inlet diaphragm having a concave shape, the piston (3; 103; 203) comprises a first part (30; 130; 230); and a second part forming a seal (40; 140; 240) which is fitted or overmoulded around at least a portion of the first part (30; 130; 230), said seal (40; 140; 240) is made of a flexible material compared to the first part (30; 130; 230) of the piston (3; 103; 203) made of a rigid material, said seal (40; 140; 240) reinforcing the seal between the piston (3; 103; 203) and the side wall(s) of the cylinder body (6; 106; 206), the piston (3; 103; 203) and the inlet check valve (5; 105) forming separate piece and being arranged so as: - that, when the cylinder body (6; 106; 206) is stationary or moves to the retracted position, the inlet diaphragm is in a tight clamping position with the top of said seal (40; 140; 240) and closes the metering inlet (35; 135; 235), and - that the concave shape of the inlet diaphragm deforms elastically and opens the metering inlet (35; 135; 235) when subjected to a negative pressure generated in the metering chamber (100; 200; 300) upon displacement of the cylinder body (6; 106; 206) to its extended position. - that, when the cylinder body (6; 106; 206) is stationary or moves to the retracted position, the inlet diaphragm is in a tight clamping position with the top of said seal (40; 140; 240) and closes the metering inlet (35; 135; 235), and - that the concave shape of the inlet diaphragm deforms elastically and opens the metering inlet (35; 135; 235) when subjected to a negative pressure generated in the metering chamber (100; 200; 300) upon displacement of the cylinder body (6; 106; 206) to its extended position.