A synthetic-resin outer cylinder (2) for a syringe has an open distal-end portion or an injection needle fixed to a distal-end portion thereof and is sterilized by radioactive rays or electron beams. The synthetic resin forming the outer cylinder contains a phenol-based antioxidant. The amount of phenoxyl radicals of the synthetic resin measured by the electron spin resonance apparatus is 0.1 to 1.0 × 10 12 spins/mg.