A syringe (1B) is provided with an inner tube (2B) which has at the tip thereof a mouth section (221) through which liquid can enter and exit the inner tube a bag body (3B) which is disposed inside the inner tube (2B) and is flexible and reversible a gasket (6) which is mounted to the tip of the inner tube (2B) and an outer tube (4) in which the inner tube (2B) is inserted together with the gasket (6) so as to be movable in the axial direction. The syringe (1B) is configured in such a manner that, when liquid (Q) enters and exits through the mouth section (221), the bag body (3B) is reversed to change the volume of a containing space (21) surrounded by the inner tube (2B) and the bag body (2B).
