A syringe protective device is provided with an outer cylinder body 4, an inner cylinder body 1, and a spring 3. When the spring 3 is released from a compressed state, the inner cylinder body 1 moves backward relative to the outer cylinder body 4 such that a syringe needle 202 is received within the outer cylinder body 4. The syringe protective device is provided with an unlockable pre-lock mechanism which affixes the inner cylinder body 1 to the outer cylinder body 4 while the spring 3 is maintained compressed in the front-rear direction. The pre-lock mechanism is configured so that the inner cylinder body 1 before being moved will be affixed to the outer cylinder body 4 by engaging the protrusion 22 of a ring body 2 with the engagement section of a through-groove section 42.
