The medicine solution 1 includes a prefilled syringe 10 and a gasket urging member assembly 20.The biasing member assembly comprises a gasket pressing member 5 for pressing the gasket 3, a flange mounting member 7 mounted on a prefilled syringe, an urging member 6 accommodated between the pressing member and the flange mounting member, and an operating member 9 having an engagement holding portion 93.The pressing member 5 is provided with an engaging portion 541 to be engaged with the flange mounting member, and the engaging portion 541 is provided with an abutting portion 542 to receive the engagement state holding portion, thereby restricting the deformation and retaining the engagement between the engaging portion 541 and the flange mounting member 7.薬液投与具１は、プレフィルドシリンジ１０とガスケット付勢部材組立体２０を備える。付勢部材組立体は、ガスケット３を押圧するガスケット押圧部材５と、プレフィルドシリンジに装着されたフランジ装着部材７と、押圧部材とフランジ装着部材間に収納された付勢部材６と、係合保持部９３を有する操作部材９を備える。押圧部材５は、フランジ装着部材と係合する係合部５４１を備え、係合部５４１は、当接部５４２を備え、係合状態保持部を受け入れることにより、変形が規制され、係合部５４１とフランジ装着部材７との係合状態を保持する。
