The present invention provides a needle unit configured to be mounted to medical syringe, the needle unit including a needle member having a longitudinally extending inner space and having a needle hole formed in a side surface of a front end and an opening formed in a base end, the inner space being in communication with the outside through the needle hole and the opening, a base portion for supporting the base end of the needle member and communicating between the syringe and the inner space of the needle member by being attached to the syringe, a slide member movable along an outer peripheral surface of the needle member and capable of taking a first position to close the needle hole and a second position to uncover the needle hole in the base end portion side of the first position, a biasing member that biases the slide member from the second position side to the first position side； and a cap removably mounted to the base portion and is configured to cover the needle member.
