1. A method of inspecting a liquid article comprising: performing a DR imaging on the liquid article to generate a transmission image; determining from the transmission image at least one positions at which CT scan is to be performed; performing dual-energy CT scan at the determined positions in a vertical direction to generate CT image data; determining a density and atomic number from the generated CT image data; comparing the density and atomic number determined from the CT image data with the respective reference density and atomic number preset in a database; and outputting information indicative of that the liquid article conceals drug if the comparison results satisfy a predetermined condition; wherein the step of determining comprises: displaying the transmission image; and receiving the at least one positions set with respect to the transmission image using an input device, and in the case of the transmission image shows that the liquid are layered, at least one line in each layer of the liquid portions is set as the positions.