A device for checking the tightness of a sealing component, such as a membrane or a multilayer, for a fluid storage tank, wherein the checking device comprises a box comprising: - a peripheral partition, - a cover made of a transparent material, the cover being connected to the peripheral partition such that the cover and the peripheral partition are able to define, with the sealing component, an inner chamber, the peripheral partition comprising: - an inner peripheral wall having a bottom end equipped with an inner peripheral seal intended to be positioned against the sealing component all around the inner chamber; and - a depressurizing device which is connected to the inner chamber and is configured to depressurize said inner chamber, the checking device being characterized in that the peripheral partition comprises an outer peripheral wall positioned outside the inner peripheral wall so as to define, between the outer peripheral wall and the inner peripheral wall, an intermediate chamber extending exclusively in the peripheral partition all around the inner chamber, the outer peripheral wall having a bottom end equipped with an outer peripheral seal intended to be positioned against the sealing component all around the inner peripheral seal; the depressurizing device being furthermore connected to the intermediate chamber and being configured to depressurize said intermediate chamber, the checking device comprising an air evacuation pipe which is connected, on one side, to a depressurizing member of the depressurizing device and, on the other side, to the intermediate chamber so as to set the intermediate chamber at a pressure P1 lower than atmospheric pressure, the inner peripheral wall comprising a communication channel fluidically connecting the inner chamber and the intermediate chamber. - a peripheral partition, - a cover made of a transparent material, the cover being connected to the peripheral partition such that the cover and the peripheral partition are able to define, with the sealing component, an inner chamber, the peripheral partition comprising: - an inner peripheral wall having a bottom end equipped with an inner peripheral seal intended to be positioned against the sealing component all around the inner chamber; and - a depressurizing device which is connected to the inner chamber and is configured to depressurize said inner chamber, - an inner peripheral wall having a bottom end equipped with an inner peripheral seal intended to be positioned against the sealing component all around the inner chamber; and - a depressurizing device which is connected to the inner chamber and is configured to depressurize said inner chamber, the checking device being characterized in that the peripheral partition comprises an outer peripheral wall positioned outside the inner peripheral wall so as to define, between the outer peripheral wall and the inner peripheral wall, an intermediate chamber extending exclusively in the peripheral partition all around the inner chamber, the outer peripheral wall having a bottom end equipped with an outer peripheral seal intended to be positioned against the sealing component all around the inner peripheral seal; the depressurizing device being furthermore connected to the intermediate chamber and being configured to depressurize said intermediate chamber, the checking device comprising an air evacuation pipe which is connected, on one side, to a depressurizing member of the depressurizing device and, on the other side, to the intermediate chamber so as to set the intermediate chamber at a pressure P1 lower than atmospheric pressure, the inner peripheral wall comprising a communication channel fluidically connecting the inner chamber and the intermediate chamber.