A syringe (and a prefilled syringe) of a structure with ventilation means allowing a pusher to be easily pushed or pulled in use, providing an excellent operability of discharging (injecting) chemicals, making it hard for foreign matter such as dirt and dust to enter into a syringe outer tube when not in use during storage or transporation, capable of assuring, by itself, the sanitation of the syringe outer tube when not in use, and allowed to be shipped without individually packaging the syringe with packaging material, wherein, as more desirable embodiments, the aseptic condition in the outer tube can be surely maintained even if the push and pull operations of the pusher are performed and, even if the pusher is pushed when not in use, a gasket does not move in tip direction and the arrangement of the pusher at the time of shipping can be stably maintained.