An inexpensive rotary grinding tool with reduced noise level of the grinding is provided. The rotary grinding tool comprises a metal disk having a grinding surface on at least a part of its surface and a holder for supporting the metal disk. The grinding surface has hard grains having a Mohs hardness in excess of 9 brazed thereon at a surface density of at least 20 grains/cm2. The holder has at its center a securing means for securing the holder on rotary shaft of a rotary drive unit. The holder and the metal disk are joined together to constitute the rotary grinding tool.