A needle assembly comprising a needle having a cutting blade formed in a distal end, a hub for holding a proximal end portion of the needle, and a distal end guarding portion, the distal end guarding portion having a mechanism for flexing the needle tip, wherein the distal end of the needle is guarded, when the distal end guarding portion is moved to a position to guard the distal end of the needle, by the needle tip being flexed by the mechanism to house the needle tip in the interior of the distal end guarding portion, the needle assembly comprising: a restraining portion for restricting a distance between the distal end guarding portion and the hub; and, a fixing portion connected to the distal end guarding portion, wherein the distal end guarding portion has a first aperture portion arranged at a proximal end of the needle, a second aperture portion arranged at a distal end of the needle, and a needle tip retraction preventing portion arranged at the second aperture portion; and, wherein the needle, in a pre-usage stage, is inserted into the distal end guarding portion from the first aperture portion of the distal end guarding portion to project from the second aperture portion, and after usage, moves from the second aperture portion by the needle, which is in contact with the needle tip retraction preventing portion, flexing, and the distal end of the needle is guarded by the needle tip being housed inside the distal end guarding portion in a state of being engaged with the distal end guarding portion, the needle assembly being characterized in that an opening of the first aperture portion and an opening of the second aperture portion form an approximate right angle with respect to each other, and in that the distal end guarding portion is connected to the fixing portion via a hinge portion, the distal end guarding portion rotating via the hinge portion with respect to the fixing portion. a restraining portion for restricting a distance between the distal end guarding portion and the hub; and, a fixing portion connected to the distal end guarding portion, wherein the distal end guarding portion has a first aperture portion arranged at a proximal end of the needle, a second aperture portion arranged at a distal end of the needle, and a needle tip retraction preventing portion arranged at the second aperture portion; and, wherein the needle, in a pre-usage stage, is inserted into the distal end guarding portion from the first aperture portion of the distal end guarding portion to project from the second aperture portion, and after usage, moves from the second aperture portion by the needle, which is in contact with the needle tip retraction preventing portion, flexing, and the distal end of the needle is guarded by the needle tip being housed inside the distal end guarding portion in a state of being engaged with the distal end guarding portion, the needle assembly being characterized in that an opening of the first aperture portion and an opening of the second aperture portion form an approximate right angle with respect to each other, and in that the distal end guarding portion is connected to the fixing portion via a hinge portion, the distal end guarding portion rotating via the hinge portion with respect to the fixing portion.