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engagement members 11 of the cover 6 engage the injection needle 5 so as to prevent the injection needle 5 from being withdrawn from the elastic engagement members 11 of the cover in a retracted state toward the base end, and the elastic engagement members and injection needle are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.
