A rotary impact tool comprising: a spindle including a rotary axis (Ax); an anvil arranged coaxially with the rotary axis (Ax) in front of the spindle; a main hammer directly or indirectly coupled to the spindle, wherein the main hammer is rotatable about the rotary axis (Ax) and movable in the axial direction, and the main hammer is configured to engage and strike the anvil to rotate the anvil; a sub-hammer that accommodates at least a portion of the main hammer and at least a portion of the spindle, wherein the sub-hammer is configured to rotate integrally with the main hammer; and the rotary impact tool being characterized by a brushless motor that is configured to rotate the spindle; and wherein the sub-hammer includes a cylindrical tube surrounding the main hammer, and wherein the rotary impact tool further comprises: at least one first groove formed on the outer circumferential surface of the main hammer and at least one second groove formed on the inner circumferential surface of the cylindrical tube of the sub-hammer, wherein each of the first groove and the second groove has a semi-circular cross section and is formed in parallel with the rotary axis (Ax) of the spindle, the first groove and the second groove are configured to form a circular hole in the collaboration with each other, an engagement element is fitted in the circular hole formed by the first groove and the second groove, the engagement element is a long member, and wherein the engagement element includes a pin serving as a core material, a cylindrical, elastic inner cover, and a metal outer cover, wherein the elastic inner cover covering the outer periphery of the pin, and the metal outer cover covering the outer periphery of the inner cover. a spindle including a rotary axis (Ax); an anvil arranged coaxially with the rotary axis (Ax) in front of the spindle; a main hammer directly or indirectly coupled to the spindle, wherein the main hammer is rotatable about the rotary axis (Ax) and movable in the axial direction, and the main hammer is configured to engage and strike the anvil to rotate the anvil; a sub-hammer that accommodates at least a portion of the main hammer and at least a portion of the spindle, wherein the sub-hammer is configured to rotate integrally with the main hammer; and the rotary impact tool being characterized by a brushless motor that is configured to rotate the spindle; and wherein the sub-hammer includes a cylindrical tube surrounding the main hammer, and wherein the rotary impact tool further comprises: at least one first groove formed on the outer circumferential surface of the main hammer and at least one second groove formed on the inner circumferential surface of the cylindrical tube of the sub-hammer, wherein each of the first groove and the second groove has a semi-circular cross section and is formed in parallel with the rotary axis (Ax) of the spindle, the first groove and the second groove are configured to form a circular hole in the collaboration with each other, an engagement element is fitted in the circular hole formed by the first groove and the second groove, the engagement element is a long member, and wherein the engagement element includes a pin serving as a core material, a cylindrical, elastic inner cover, and a metal outer cover, at least one first groove formed on the outer circumferential surface of the main hammer and at least one second groove formed on the inner circumferential surface of the cylindrical tube of the sub-hammer, wherein each of the first groove and the second groove has a semi-circular cross section and is formed in parallel with the rotary axis (Ax) of the spindle, the first groove and the second groove are configured to form a circular hole in the collaboration with each other, an engagement element is fitted in the circular hole formed by the first groove and the second groove, the engagement element is a long member, and wherein the engagement element includes a pin serving as a core material, a cylindrical, elastic inner cover, and a metal outer cover, wherein the elastic inner cover covering the outer periphery of the pin, and the metal outer cover covering the outer periphery of the inner cover.