A drug solution administration device comprising: an injection unit that injects a drug solution in vivo; a container provided with a containing space communicated with the injection unit and configured to contain the drug solution which is to be fed to the injection unit; a push-out mechanism at least a part of which moves back and forth inside the containing space and which allows the drug solution stored inside the containing space to flow into the injection unit; a sealing member attached to the push-out mechanism and pressed against a wall surface of the containing space to prevent leakage of the drug solution inside the containing space from the push-out mechanism; a drive mechanism that generates a drive force for moving the push-out mechanism back and forth; and a control unit that commands the drive mechanism to start an operation and to stop the operation, wherein, when a predetermined time has passed after the command to stop the operation of the drive mechanism, the control unit controls the drive mechanism to move the push-out mechanism and the sealing member in the opposite direction as a direction in which the drug solution is fed and to shift a position of the sealing member relative to the wall surface of the containing space, characterized in that the injection unit and the container are configured to be connected to and/or separated from each other, the drug solution administration device further comprises a fitting detection unit that detects fitting of the container to the injection unit, and the control unit commands the drive mechanism to move the push-out mechanism and the sealing member in the opposite direction as a direction in which the drug solution is fed-when a predetermined time has passed after the command to stop the operation and when the fitting detection unit detects separation between the injection unit and the container. an injection unit that injects a drug solution in vivo; a container provided with a containing space communicated with the injection unit and configured to contain the drug solution which is to be fed to the injection unit; a push-out mechanism at least a part of which moves back and forth inside the containing space and which allows the drug solution stored inside the containing space to flow into the injection unit; a sealing member attached to the push-out mechanism and pressed against a wall surface of the containing space to prevent leakage of the drug solution inside the containing space from the push-out mechanism; a drive mechanism that generates a drive force for moving the push-out mechanism back and forth; and a control unit that commands the drive mechanism to start an operation and to stop the operation, wherein, when a predetermined time has passed after the command to stop the operation of the drive mechanism, the control unit controls the drive mechanism to move the push-out mechanism and the sealing member in the opposite direction as a direction in which the drug solution is fed and to shift a position of the sealing member relative to the wall surface of the containing space, characterized in that the injection unit and the container are configured to be connected to and/or separated from each other, the drug solution administration device further comprises a fitting detection unit that detects fitting of the container to the injection unit, and the control unit commands the drive mechanism to move the push-out mechanism and the sealing member in the opposite direction as a direction in which the drug solution is fed-when a predetermined time has passed after the command to stop the operation and when the fitting detection unit detects separation between the injection unit and the container.