A syringe (10, 10A) including an outer cylinder (14, 16) having a flowing port which allows liquid to flow therethrough at a distal end thereof, and a plunger (22, 152) to be inserted from a proximal side of the outer cylinder (14, 16) into the outer cylinder (14, 16), and being configured to push out liquid in the interior of the outer cylinder (14, 16) from the flowing port by the movement of the plunger (22, 152) in the direction toward a distal end thereof, the plunger (22, 152) comprising: a tooth portion (90, 154) provided along the direction of the movement of the plunger (22, 152); and the syringe further comprising: a locking portion (98, 158) configured to lock the tooth portion (90, 154) at a predetermined locking position to prevent the plunger (22, 152) from moving in the direction toward the proximal end thereof, wherein the locking portion (98, 158) is configured to be retracted from the locking position in association with an unlocking operation, and to be restored to the locking position automatically after the unlocking operation, wherein the locking portion (98, 158) includes a hook formed integrally with a flexible stopper member (24, 150), and the stopper member (24, 150) arranges the hook (98, 158) at the locking position by being mounted on the outer cylinder (14, 16) and includes: a mounting portion (92, 156) configured to surround an outer peripheral surface of the outer cylinder (14, 16), characterised in that the stopper member (24, 150) further includes: a pair of operating strips (94, 160) extending so as to be apart radially outward from an outer peripheral surface of the mounting portion (92, 156), wherein the hook (98, 158) is formed on an inner peripheral surface of the mounting portion (92, 156), and is configured to move radially outward under a pinching action of the pair of the operation strips (94, 160) at the time of unlocking operation and to retract from the locking position. a tooth portion (90, 154) provided along the direction of the movement of the plunger (22, 152); and the syringe further comprising: a locking portion (98, 158) configured to lock the tooth portion (90, 154) at a predetermined locking position to prevent the plunger (22, 152) from moving in the direction toward the proximal end thereof, wherein the locking portion (98, 158) is configured to be retracted from the locking position in association with an unlocking operation, and to be restored to the locking position automatically after the unlocking operation, wherein the locking portion (98, 158) includes a hook formed integrally with a flexible stopper member (24, 150), and the stopper member (24, 150) arranges the hook (98, 158) at the locking position by being mounted on the outer cylinder (14, 16) and includes: a mounting portion (92, 156) configured to surround an outer peripheral surface of the outer cylinder (14, 16), characterised in that the stopper member (24, 150) further includes: a pair of operating strips (94, 160) extending so as to be apart radially outward from an outer peripheral surface of the mounting portion (92, 156), wherein the hook (98, 158) is formed on an inner peripheral surface of the mounting portion (92, 156), and is configured to move radially outward under a pinching action of the pair of the operation strips (94, 160) at the time of unlocking operation and to retract from the locking position. a mounting portion (92, 156) configured to surround an outer peripheral surface of the outer cylinder (14, 16), characterised in that the stopper member (24, 150) further includes: a pair of operating strips (94, 160) extending so as to be apart radially outward from an outer peripheral surface of the mounting portion (92, 156), wherein the hook (98, 158) is formed on an inner peripheral surface of the mounting portion (92, 156), and is configured to move radially outward under a pinching action of the pair of the operation strips (94, 160) at the time of unlocking operation and to retract from the locking position. a pair of operating strips (94, 160) extending so as to be apart radially outward from an outer peripheral surface of the mounting portion (92, 156), wherein the hook (98, 158) is formed on an inner peripheral surface of the mounting portion (92, 156), and is configured to move radially outward under a pinching action of the pair of the operation strips (94, 160) at the time of unlocking operation and to retract from the locking position.