The objective of the present invention is to provide a next generation prefilling syringe provided with a safety mechanism for preventing needlestick injuries while reducing the number of components and reducing the cost. In the syringe according to the present invention resilient engaging pieces 11 of a cover 6 which are in a stowed position and an injection needle 5 engage with one another in such a way as to prevent the injection needle 5 from being pulled out from the resilient engaging pieces 11 to a base end side and said engagement is released by the resilient engaging pieces 11 deforming so as to expand diametrically. Further a plunger 4 is provided integrally with a deformation preventing portion 41 which covers an outer periphery of the plurality of resilient engaging pieces 11 in such a way as to prevent the resilient engaging pieces 11 from expanding diametrically and thereby releasing the engagement between the resilient engaging pieces 11 and the injection needle 5.
