PROBLEM TO BE SOLVED: To provide a pre-filled syringe made hard to loosen while enabling a plunger rod to be simply screwed on a gasket.SOLUTION: A plunger rod 20 comprises a male screw part 24 and a rod side engaging part 25. A gasket 30 comprises a female screw part 34, and a gasket side engaging part 35, with which the rod side engaging part 25 engages. One of the rod side engaging part 25 and the gasket side engaging part 35 bites the other, in the case where a relative rotation force in a loosening direction acts when the male screw part 24 and a female screw part 34 are in the engaging state.
