A digging bit for forming a borehole in rocks, comprising: a reaming portion whose diameter is larger than a rear end portion of a bit body, and which is formed in a front end portion of the bit body rotated around an axis, wherein the reaming portion is provided with a contacting surface having a circular shape around the axis, a gauge surface having a truncated cone surface shape formed around the axis which tilts toward a rear end side of the reaming portion as the gauge surface goes toward an outer peripheral side of the gauge surface, an outer peripheral surface having a truncated cone shape formed around the axis, which tilts more gently than the gauge surface toward the inner peripheral side of the gauge surface as the outer peripheral surface goes toward the rear end side of the reaming portion, and a rear end surface having a concave and curved shape in cross section along the axis, and is formed so as to come into contact with an outer peripheral surface of the rear end portion of the bit body; digging tips which are arranged in the contacting surface and the gauge surface of the reaming portion; a debris groove which extends in the axial direction, and which is formed in the outer peripheral surface of the reaming portion; and a communication groove which is connected with the debris groove, and which is formed from the outer peripheral surface to the rear end surface of the reaming portion; the digging bit is characterized in that the communication groove extends in a direction tilting to the axis and tilts toward a front end side of the reaming portion in the axial direction so as to be oriented in the rotating direction of the bit body. a reaming portion whose diameter is larger than a rear end portion of a bit body, and which is formed in a front end portion of the bit body rotated around an axis, wherein the reaming portion is provided with a contacting surface having a circular shape around the axis, a gauge surface having a truncated cone surface shape formed around the axis which tilts toward a rear end side of the reaming portion as the gauge surface goes toward an outer peripheral side of the gauge surface, an outer peripheral surface having a truncated cone shape formed around the axis, which tilts more gently than the gauge surface toward the inner peripheral side of the gauge surface as the outer peripheral surface goes toward the rear end side of the reaming portion, and a rear end surface having a concave and curved shape in cross section along the axis, and is formed so as to come into contact with an outer peripheral surface of the rear end portion of the bit body; digging tips which are arranged in the contacting surface and the gauge surface of the reaming portion; a debris groove which extends in the axial direction, and which is formed in the outer peripheral surface of the reaming portion; and a communication groove which is connected with the debris groove, and which is formed from the outer peripheral surface to the rear end surface of the reaming portion; the digging bit is characterized in that the communication groove extends in a direction tilting to the axis and tilts toward a front end side of the reaming portion in the axial direction so as to be oriented in the rotating direction of the bit body.