A drug filling machine having a plurality of feeders containing a plurality of different kinds of drugs. A plurality of the drugs are discharged from one or some of the feeders into a vial. A sealing unit is provided for sealing the mouth of the vial with a transparent sheet. The sealing unit includes a sheet presser for pushing the transparent sheet into the mouth of the vial to form a sealing sheet having a tray-shaped section, a cutter for cutting the transparent sheet into a predetermined shape, and a heater for fusing the transparent sheet to the top end of the vial to seal the mouth of the vial. A method of inspecting the drugs contained in the vial includes preparing the transparent sheet a sealing portion for covering the mouth of the vial, and a printed portion that protrudes outwardly of the mouth of the vial. After inspecting the drugs in the vial, the printed portion is separated from the sealing portion, and a cap is secured on the mouth of the vial.