A production method for a pre-filled syringe includes holding a syringe assembly； reducing a pressure in the outer barrel of the syringe assembly to a set pressure； while the pressure in the outer barrel of the syringe assembly is at the set pressure, sealing the proximal end opening of the outer barrel with the gasket by disposing the gasket at a sealing position； and pushing the gasket toward the barrel tip with a sliding motion through the outer barrel to move the gasket from the sealing position to an insertion position, and the insertion position being a position at which a distal end surface of the gasket is spaced from the drug solution. After the gasket is moved to the insertion position, a pressure in a space between the drug solution and the distal end surface of the gasket is approximately equal to the atmospheric pressure.
