A reagent-bottle lid opening mechanism is disclosed, which has a needle for piercing a lid of a reagent bottle to be delivered to a reagent disk, has an aligning mechanism of automatically adjusting a position of the needle with respect to the lid such that a needle body of the needle can stick in the center of the lid, and accurately and repeatedly makes an incision in the center of the lid. As a result, an automatic analyzer is provided that is capable of unsealing the center of the lid of the reagent bottle with accuracy even if the central axis of the needle and the central axis of the lid are offset from each other.