A safety needle assembly with a sheath, comprising: a hub including a proximal end configured to be connected with a syringe, and a distal end; a cannula including a proximal end connecting with the distal end of the hub, a lumen extending in a longitudinal direction, and a distal end; a collar attached to the hub, including a sheath attachment part and a pair of sheath fixing protrusions; a protector covering the distal end of the cannula by being attached to the hub or the collar, and being detachable to expose the distal end of the cannula; and an opening partially extending along at least a longitudinal direction of the sheath so as to house the cannula, wherein the sheath further comprises: a cannula fixing part comprised of grooves in which sheath fixing protrusions are fitted respectively when the cannula is housed in the opening, and a pair of wing walls each of which is provided with a slope arranged inside a corresponding wing wall in a direction from the grooves to the proximal end of the sheath; and an attachment part rotatably supporting the sheath in a direction of housing the cannula when the protector is detached to expose the distal end of the cannula, the attachment part being attached to the sheath attachment part of the collar, characterized in that the cannula fixing part in which the sheath fixing protrusions of the collar are fitted is arranged at the front side of the wing wall each having the slope. a hub including a proximal end configured to be connected with a syringe, and a distal end; a cannula including a proximal end connecting with the distal end of the hub, a lumen extending in a longitudinal direction, and a distal end; a collar attached to the hub, including a sheath attachment part and a pair of sheath fixing protrusions; a protector covering the distal end of the cannula by being attached to the hub or the collar, and being detachable to expose the distal end of the cannula; and an opening partially extending along at least a longitudinal direction of the sheath so as to house the cannula, wherein the sheath further comprises: a cannula fixing part comprised of grooves in which sheath fixing protrusions are fitted respectively when the cannula is housed in the opening, and a pair of wing walls each of which is provided with a slope arranged inside a corresponding wing wall in a direction from the grooves to the proximal end of the sheath; and an attachment part rotatably supporting the sheath in a direction of housing the cannula when the protector is detached to expose the distal end of the cannula, the attachment part being attached to the sheath attachment part of the collar, characterized in that the cannula fixing part in which the sheath fixing protrusions of the collar are fitted is arranged at the front side of the wing wall each having the slope. a cannula fixing part comprised of grooves in which sheath fixing protrusions are fitted respectively when the cannula is housed in the opening, and a pair of wing walls each of which is provided with a slope arranged inside a corresponding wing wall in a direction from the grooves to the proximal end of the sheath; and an attachment part rotatably supporting the sheath in a direction of housing the cannula when the protector is detached to expose the distal end of the cannula, the attachment part being attached to the sheath attachment part of the collar, characterized in that the cannula fixing part in which the sheath fixing protrusions of the collar are fitted is arranged at the front side of the wing wall each having the slope.