Provided is an interdental brush having a wire and filaments arranged therein by folding the wire and disposing the filaments between the wire and then twisting the wire. The interdental brush has improved filament retention and improved cleaning effectivity and reachability to minute portions. Each of filaments 3 has a polygonal cross section whose at least one corner portion has an interior angle 31 as acute as 30 to 75 degrees. Specifically, an angle θ3 of the acute corner portion 31 is set at 1.2 to 3 times a twisting angle θ4 of the wire. The filaments each have two or more such acute corner portions, and two or more rows of such filaments are disposed and laminated between the wire in a densely arranged manner.