An injection device comprises: a drug storer having a first space for storing a drug； a unidirectional switch having a second space in fluid communication with the first space； and an injection body having a third space in fluid communication with the second space, wherein the third space is provided with a piston adapted to move along the injection body, and to pump the drug stored in the first space into the third space. The drug storer comprises a base and a head cover, and at least one of the base and the head cover is formed by a flexible film, thereby forming the first space for storing a drug.
