The present invention provides a next-generation pre-filled syringe having a reduced number of components and requiring reduced costs and including a safety mechanism for preventing needlestick injuries. In the syringe of the present invention, elastic engagement members (11) of the cover (6) engage the injection needle (5) so as to prevent the injection needle (5) from being withdrawn from the elastic engagement members (11) of the cover in a retracted state toward the base end, and the elastic engagement members (11) and injection needle (5) are disengaged from each other as the elastic engagement members (11) are diametrically expanded/deformed. Further, the plunger (4) includes an integrated deformation-prevention part (41) covering the outer peripheries of the plurality of elastic engagement members (11) so as to prevent the elastic engagement members (11) and the injection needle (5) from being disengaged from each other as the elastic engagement members (11) are diametrically expanded/deformed.
