Operability and lifespan of a drain valve of an operated infusion device are improved when changing the composition of a transported solution or releasing the pressure. A sealing portion and a shaft portion of the valve are constructed to be separated from each other. The shaft portion is disposed with a through hole having a step. A screw passes through the through hole, such that a screw portion of the screw is screwed to the sealing portion, and on the other hand, a screw head is fastened to the step portion of the through hole of the shaft portion. The sealing portion and the shaft portion can ensure a degree of freedom of rotation while maintaining a fixed position relationship there-between, thereby preventing the sealing portion from falling off and prolonging the lifespan of a valve body.
