There is provided a liquid administration device 10 including: an inner structure 1 that includes a cylindrical body 2 which can be filled with a liquid therein, a needle tube which is mounted in a distal portion of the cylindrical body 2, and a gasket 8 an operation member 5 which has a plunger 51 pressing the gasket 8 and performs a pressing operation through which the plunger 51 is moved to the cylindrical body 2 toward a distal direction while being pressed an engagement portion that includes a first engagement portion which is provided in one of the inner structure 1 and the operation member 5 and a second engagement portion which is provided in the other one of the inner structure and the operation member, in which the engagement portion enters an engagement state where the pressing operation is inhibited when the first engagement portion and the second engagement portion are engaged with each other, and enters a released state where the pressing operation can be performed when the engagement state is released and a rotary portion which makes the first engagement portion and the second engagement portion, being in the engagement state, relatively rotate around a central axis of the inner structure 1 and enter the released state.
