An endodontic file with an improved fracturable area for dental nerve treatment, the endodontic file comprising: a helical shaped blade that is to be inserted into a root canal, remove dental nerve, and enlarge the root canal; a head that is detachably inserted into a rotary power tool, and a connection part extending by a predetermined length between the head and the blade and having a diameter smaller than that of each of a contact end of the blade and the head , wherein the connection part is formed with a plurality of slit that are recessed at regular intervals along a longitudinal direction of the connection part along a circumference of the surface of the connection part , and characterized in that a cross section of the slit is provided with: a first rounded section extended to protrude from a portion where a recess starts toward a center of the slit to be rounded with a first radius of curvature; a second rounded section extended to be recessed from an end of the first rounded section toward a bottom surface of the slit with a second radius of curvature that is larger than the first radius of curvature, and a third rounded section protruding from an end portion where the second rounded section and a second rounded section of a cross section of an adjacent slit meet each other toward a portion where the recess start, with a third radius of curvature that is smaller than the first and the second radius of curvature. a helical shaped blade that is to be inserted into a root canal, remove dental nerve, and enlarge the root canal; a head that is detachably inserted into a rotary power tool, and a connection part extending by a predetermined length between the head and the blade and having a diameter smaller than that of each of a contact end of the blade and the head , wherein the connection part is formed with a plurality of slit that are recessed at regular intervals along a longitudinal direction of the connection part along a circumference of the surface of the connection part , and characterized in that a cross section of the slit is provided with: a first rounded section extended to protrude from a portion where a recess starts toward a center of the slit to be rounded with a first radius of curvature; a second rounded section extended to be recessed from an end of the first rounded section toward a bottom surface of the slit with a second radius of curvature that is larger than the first radius of curvature, and a third rounded section protruding from an end portion where the second rounded section and a second rounded section of a cross section of an adjacent slit meet each other toward a portion where the recess start, with a third radius of curvature that is smaller than the first and the second radius of curvature. a first rounded section extended to protrude from a portion where a recess starts toward a center of the slit to be rounded with a first radius of curvature; a second rounded section extended to be recessed from an end of the first rounded section toward a bottom surface of the slit with a second radius of curvature that is larger than the first radius of curvature, and a third rounded section protruding from an end portion where the second rounded section and a second rounded section of a cross section of an adjacent slit meet each other toward a portion where the recess start, with a third radius of curvature that is smaller than the first and the second radius of curvature. <EOS>