The syringe includes first and second outer cylinders having a flowing port at a distal end through which liquid is flowable, and a plunger inserted from the proximal side of the outer cylinder. The syringe includes a tooth portion provided along the direction of movement of the plunger, and a hook configured to lock the tooth portion at a predetermined locking position and prevent the movement of the plunger in the direction toward the proximal end. The hook retracts from the locking position in association with the unlocking operation and restores automatically to the locking position after the unlocking operation.
