An impact rotation tool including: a drive shaft rotated and driven by a rotational power source, wherein the drive shaft includes a drive shaft hole; an anvil that is coaxial with the drive shaft and rotatable relative to the drive shaft, wherein the anvil includes an anvil hole; a hammer rotated by the drive shaft and engaged with the anvil, wherein the hammer is coupled to the drive shaft so that the hammer moves away from the anvil in an axial direction of the drive shaft when the hammer rotates relative to the drive shaft; an urging member that urges the hammer toward the anvil; and a switching mechanism that switches the impact rotation tool between an impact mode that impacts the anvil with the hammer and a drill mode that integrally rotates the drive shaft and the anvil, wherein the switching mechanism includes a coupling member movable between a position where the coupling member is engaged with a wall of only one of the drive shaft hole and the anvil hole and a position where the coupling member is engaged with the walls of both of the drive shaft hole and the anvil hole, a switching shaft that supports the coupling member to be rotatable and moves the coupling member in the axial direction, and a stopper that restricts axial movement of the coupling member relative to the switching shaft; and wherein the switching shaft moves the coupling member to the position where the coupling member is engaged with the wall of only the drive shaft hole to switch to the impact mode, and wherein the switching shaft moves the coupling member to the position where the coupling member is engaged with the walls of both of the drive shaft hole and the anvil hole to switch to the drill mode, and wherein the wall of the drive shaft hole includes an engagement portion engaged with the coupling member in the impact mode, and the impact rotation tool being characterised in that the wall of the drive shaft hole further includes a relief formed so as not to contact an outer circumferential surface of the coupling member in the impact mode. a drive shaft rotated and driven by a rotational power source, wherein the drive shaft includes a drive shaft hole; an anvil that is coaxial with the drive shaft and rotatable relative to the drive shaft, wherein the anvil includes an anvil hole; a hammer rotated by the drive shaft and engaged with the anvil, wherein the hammer is coupled to the drive shaft so that the hammer moves away from the anvil in an axial direction of the drive shaft when the hammer rotates relative to the drive shaft; an urging member that urges the hammer toward the anvil; and a switching mechanism that switches the impact rotation tool between an impact mode that impacts the anvil with the hammer and a drill mode that integrally rotates the drive shaft and the anvil, wherein the switching mechanism includes a coupling member movable between a position where the coupling member is engaged with a wall of only one of the drive shaft hole and the anvil hole and a position where the coupling member is engaged with the walls of both of the drive shaft hole and the anvil hole, a switching shaft that supports the coupling member to be rotatable and moves the coupling member in the axial direction, and a stopper that restricts axial movement of the coupling member relative to the switching shaft; and wherein the switching shaft moves the coupling member to the position where the coupling member is engaged with the wall of only the drive shaft hole to switch to the impact mode, and wherein the switching shaft moves the coupling member to the position where the coupling member is engaged with the walls of both of the drive shaft hole and the anvil hole to switch to the drill mode, and wherein the wall of the drive shaft hole includes an engagement portion engaged with the coupling member in the impact mode, and the impact rotation tool being characterised in that the wall of the drive shaft hole further includes a relief formed so as not to contact an outer circumferential surface of the coupling member in the impact mode.