A drill comprising: a drill main body ; a plurality of cutting edges which are formed on a tip side of the drill main body from an outer periphery of the drill main body to a chisel edge provided near to a rotational axis (O); thinnings which are each formed between the cutting edges; flutes which are each formed from a posterior end of each of the thinnings in a direction of the rotational axis (O) toward a posterior end side of the drill main body ; first margins which are each formed along an outer peripheral end of the drill main body on a back side of each of the flutes in a rotational direction (R); second margins which are each formed along the outer peripheral end of the drill main body on a forward side of each of the flutes in the rotational direction (R); second faces which are each formed in an approximately band shape and are each formed along each of the cutting edges on a back side of the cutting edge in the rotational direction (R); third faces which are each formed to be continuous with a back side of each of the second faces in the rotational direction (R); and fourth faces which are each formed to be continuous with a back side of each of the third faces in the rotational direction (R); wherein a tip side of each of the thinnings is continuous with the back side of each of the third faces in the rotational direction (R), a posterior end side of each of the thinnings is continuous with a back side of each of the fourth faces in the rotational direction (R), characterised in that the cutting edges extend in a convex-arc shape from the outer periphery of the tip portion to the chisel edge , and in a case where the drill main body is viewed from the tip side thereof, each of boundaries between the thinnings and the third faces forms an angle (ε) of 35° to 55° with each of boundaries between the thinnings and the fourth faces . a drill main body ; a plurality of cutting edges which are formed on a tip side of the drill main body from an outer periphery of the drill main body to a chisel edge provided near to a rotational axis (O); thinnings which are each formed between the cutting edges; flutes which are each formed from a posterior end of each of the thinnings in a direction of the rotational axis (O) toward a posterior end side of the drill main body ; first margins which are each formed along an outer peripheral end of the drill main body on a back side of each of the flutes in a rotational direction (R); second margins which are each formed along the outer peripheral end of the drill main body on a forward side of each of the flutes in the rotational direction (R); second faces which are each formed in an approximately band shape and are each formed along each of the cutting edges on a back side of the cutting edge in the rotational direction (R); third faces which are each formed to be continuous with a back side of each of the second faces in the rotational direction (R); and fourth faces which are each formed to be continuous with a back side of each of the third faces in the rotational direction (R); wherein a tip side of each of the thinnings is continuous with the back side of each of the third faces in the rotational direction (R), a posterior end side of each of the thinnings is continuous with a back side of each of the fourth faces in the rotational direction (R), characterised in that the cutting edges extend in a convex-arc shape from the outer periphery of the tip portion to the chisel edge , and in a case where the drill main body is viewed from the tip side thereof, each of boundaries between the thinnings and the third faces forms an angle (ε) of 35° to 55° with each of boundaries between the thinnings and the fourth faces . <EOS>