This helical broach forms a twisted groove at the inner periphery of a machined hole of a work by means of a plurality of cutting blades. The plurality of cutting blades have: a plurality of groove depth-expanding blades that are arrayed towards the tip of a broach body; and a plurality of groove width-expanding blades that are arrayed towards the base of the broach body. The plurality of groove width-expanding blades have a cutting blade and a guiding blade. The groove width-expanding blade positioned furthest towards the base of the broach body is formed with a guiding blade instead of a cutting blade at the edge of intersection of a scooping surface and the lateral surface that faces one of the wall surfaces from among both groove wall surfaces of the twisted groove of the work.
