A prefilled syringe comprising: a syringe barrel including a syringe barrel body and an outer barrel, the syringe barrel body having a drug solution discharge portion located on a tip end and an insertion port open on a base end, at least a part of the outer barrel extending in a tubular shape from the insertion port toward a base end side, the outer barrel having an opening located on a base end and having an inner diameter that is larger than an inner diameter of the syringe barrel body in a region between the insertion port and the opening; a cap configured to seal the drug solution discharge portion; a gasket disposed in the syringe barrel body; a plunger having a shaft disposed in the syringe barrel through the opening and a press portion disposed on a base end of the shaft, the plunger being configured to move toward the tip end by a pressing operation to the press portion to allow the gasket to slide toward the drug solution discharge portion; and a drug solution stored between the drug solution discharge portion and the gasket inside the syringe barrel body, the drug solution being dischargeable from the drug solution discharge portion by the sliding of the gasket, wherein the outer barrel includes a window formed on a wall of the outer barrel located between the insertion port and the opening of the outer barrel, and a mask configured to hide an inside of the outer barrel, characterized in that a mark is disposed on a part of the shaft located between the insertion port and the opening of the outer barrel, the mark having an outer diameter larger than the inner diameter of the syringe barrel body, at least an outer peripheral surface of the mark having a color that is different from a color of other parts of the plunger, wherein, before discharge of the drug solution, the outer peripheral surface of the mark is covered with the mask such that the mark is not visually recognizable through the window from a direction inclined by 70° or more with respect to a central axis of the outer barrel, and wherein, after discharge of the drug solution is completed, the outer peripheral surface of the mark which has moved along with movement of the plunger toward the tip end, is visually recognizable through the window. a syringe barrel including a syringe barrel body and an outer barrel, the syringe barrel body having a drug solution discharge portion located on a tip end and an insertion port open on a base end, at least a part of the outer barrel extending in a tubular shape from the insertion port toward a base end side, the outer barrel having an opening located on a base end and having an inner diameter that is larger than an inner diameter of the syringe barrel body in a region between the insertion port and the opening; a cap configured to seal the drug solution discharge portion; a gasket disposed in the syringe barrel body; a plunger having a shaft disposed in the syringe barrel through the opening and a press portion disposed on a base end of the shaft, the plunger being configured to move toward the tip end by a pressing operation to the press portion to allow the gasket to slide toward the drug solution discharge portion; and a drug solution stored between the drug solution discharge portion and the gasket inside the syringe barrel body, the drug solution being dischargeable from the drug solution discharge portion by the sliding of the gasket, wherein the outer barrel includes a window formed on a wall of the outer barrel located between the insertion port and the opening of the outer barrel, and a mask configured to hide an inside of the outer barrel, the outer barrel includes a window formed on a wall of the outer barrel located between the insertion port and the opening of the outer barrel, and a mask configured to hide an inside of the outer barrel, characterized in that a mark is disposed on a part of the shaft located between the insertion port and the opening of the outer barrel, the mark having an outer diameter larger than the inner diameter of the syringe barrel body, at least an outer peripheral surface of the mark having a color that is different from a color of other parts of the plunger, wherein, before discharge of the drug solution, the outer peripheral surface of the mark is covered with the mask such that the mark is not visually recognizable through the window from a direction inclined by 70° or more with respect to a central axis of the outer barrel, and wherein, after discharge of the drug solution is completed, the outer peripheral surface of the mark which has moved along with movement of the plunger toward the tip end, is visually recognizable through the window.