A chamfering tool that chamfers an opening edge of a target hole formed in a work, the chamfering tool including a support shaft, a base shaft having the support shaft on a tip end side thereof and being eccentric with respect to the support shaft, and a blade portion having a rake face that is a step surface of a step protrusion portion protruded laterally from the support shaft or that is an end surface of the support shaft. The blade portion including an edge line in a shape of a curve and being bulged to a side away from a center axis of the support shaft, and the edge line being inclined with respect to an axial direction of the support shaft.