To perform a rounding process for all the bristle tips with different heights by a method wherein a grinding element having a tapered-in edge, and a grinding element driving unit to perform a rounding process for bristle tips at a low part by slidably bringing the edge into contact with the bristle tips at the low part under a state wherein the edge of the grinding element is being moved, are provided.

A toothbrush 14 is cut into a mountain-valley shape by a bristle cutter, and the bristle tips 14a1 are ground into a conical shape by a conical grinder of a conical grinder rounding device. Then, the bristle tips are made into a semi-spherical shape by a flat grinder rounding device. Then, at a valley-shaped part grinder rounding device, the peripheral edge part 40c of a grinder 40 being rotated, is pressed to the bristle tips 14a1 of the toothbrush 14, and the grinder 40 is made to reciprocate at a right angle to the longitudinal direction of the toothbrush 14. By doing so, the peripheral edge part 40c of the grinder 40 having a tapered-in edge, is slidably brought into contact with the bristle tips at a valley part 14e of the brush, and a rounding process for the bristle tips, is performed. As a result, even the valley part 14e of the brush 14, to which a conical grinder and a rotary flat grinder cannot reach, can be surely rounded.