The present invention relates to a dental root canal therapeutic instrument comprising: a shaft portion and a work portion made of spiral projections in continuation with the shaft portion. A cross section of the projections of the work portion is formed of a set of long sides and a set of short sides and is composed of a parallelogram constituted of a set of acute angle edges and a set of obtuse angle edges, wherein the acute angle edges among the acute angle edges and the obtuse angle edges, which form the projections, are placed on a side of the shaft on the side face of the work portion, and wherein a tip of the acute angle edge is located at a further position with respect to a center axis of the work portion than a position of a tip of the obtuse angle edge.
