The present invention miniaturizes an entire device. In the present invention, a piston 21 is arranged at an initial position where the piston is further pulled back from a pulled-back position and where a part of a front end part 21A formed in a truncated cone shape contacts with a packing 27 along a circumferential direction in an initial state. The amount of the squeeze of the packing 27 is reduced when the piston 21 is located at the initial position by pulling back and locating the piston 21 before medical solution is inserted into a medical solution storage unit 6. Therefore, a contact resistance can be reduced than that in a case where the packing 27 contacts with a body 21B of the piston 21. Accordingly, it is not necessary to use a large force to start the piston by receiving a starting resistance at the time of starting the use of it, and the entire device can be miniaturized.
