The present invention provides an automatic drug delivery device. The automatic drug delivery device includes an enclosure and a first piston disposed in the enclosure. The first piston partitions the enclosure to a first drug delivery chamber and a first expansion chamber. A first through hole and a second through hole are formed in the wall of the enclosure, the first through-hole communicates with the first drug delivery chamber, and the second through-hole communicates with the first expansion chamber. A first targeted dissolution membrane covers the first through hole and the second through hole, and dissolves at a first targeted region. A drug is filled in the first drug delivery chamber, and an expandable material is included in the first expansion chamber. The expandable material in the first expansion chamber can expand after absorbing liquid.
