An injector includes a hollow needle; a main body unit including a needle holding portion that holds the needle; and a protection device configured to cover the needle before and after puncturing a puncture target with the needle. The protection device includes: an inner member attached to the needle holding portion and being freely rotatable around an outer periphery of the needle holding portion; and an outer member configured to (i) cover an outer side of the needle and the inner member before puncturing, (ii) expose the needle by moving toward a proximal end side relative to the main body unit at a time of puncturing, and (iii) cover a distal end of the needle by moving toward a distal end side relative to the main body unit after puncturing.