Provided is an interdental brush having a wire and filamentsarranged therein by folding the wire and disposing the filaments betweenthe wire and then twisting the wire. The interdental brush has improvedfilament retention and improved cleaning effectivity and reachability tominute portions. Each of filaments 3 has a polygonal cross section whoseat least one corner portion has an interior angle 31 as acute as 30 to 75degrees. Specifically, an angle .theta.3 of the acute corner portion 31 is setat 1.2to 3 times a twisting angle .theta.4 of the wire. The filaments each have twoormore such acute corner portions, and two or more rows of such filaments aredisposed and laminated between the wire in a densely arranged manner.
