A method for quenching a steel pipe, the method comprising the steps of: conveying a steel pipe onto a rotatable supporting member using a walking-arm type revolving conveyance apparatus; and rapidly cooling the steel pipe with first spray nozzles disposed above the pipe while the steel pipe is being rotated about a pipe axis of the steel pipe on the rotatable supporting member in a state where movements of the steel pipe in a direction parallel to and in a direction perpendicular to the pipe axis are stopped, the first spray nozzles being disposed along an axial direction of the steel pipe with an angle of 20 to 70° from the uppermost part of the pipe in a circumferential direction, the first spray nozzles being disposed except a swept range W of the walking-arm type revolving conveyance apparatus in a longitudinal direction of the steel pipe, the first spray nozzles including inclined spray nozzles that are disposed by being tilted toward the swept range W, and flat spray nozzles that are disposed adjacent to the inclined spray nozzles at equal intervals with a predetermined pitch D in the longitudinal direction of the steel pipe, wherein the flat spray nozzles have a spray-water distribution in line symmetry with respect to the center axis of the nozzle and the inclined spray nozzles have a spray-water distribution in line asymmetry with respect to the center axis of the nozzle, the inclined spray nozzles being disposed by being offset by a distance S from the predetermined pitch D, and being tilted with an angle θ of 30° or less, where the angle θ is determined in terms of the relationship θ = arctan(S/H), where S is the distance from the predetermined pitch D of the flat spray nozzles and H is an injection height of the first spray nozzles, wherein the first spray nozzles disposed above the pipe are disposed opposite to each other across the longitudinal direction of the steel pipe lying in the middle, wherein the first spray nozzles disposed above the pipe are disposed opposite to each other with offset of a pitch of D/4 to 3D/4 along the longitudinal direction of the steel pipe, wherein the walking-arm type revolving conveyance apparatus includes a pipe hold-down member that holds down the steel pipe rotating on the rotatable supporting member, and wherein the walking-arm type revolving conveyance apparatus includes second spray nozzles that rapidly cool a region where the first spray nozzles disposed above the pipe interfere with the pipe hold-down member. conveying a steel pipe onto a rotatable supporting member using a walking-arm type revolving conveyance apparatus; and rapidly cooling the steel pipe with first spray nozzles disposed above the pipe while the steel pipe is being rotated about a pipe axis of the steel pipe on the rotatable supporting member in a state where movements of the steel pipe in a direction parallel to and in a direction perpendicular to the pipe axis are stopped, the first spray nozzles being disposed along an axial direction of the steel pipe with an angle of 20 to 70° from the uppermost part of the pipe in a circumferential direction, the first spray nozzles being disposed except a swept range W of the walking-arm type revolving conveyance apparatus in a longitudinal direction of the steel pipe, the first spray nozzles including inclined spray nozzles that are disposed by being tilted toward the swept range W, and flat spray nozzles that are disposed adjacent to the inclined spray nozzles at equal intervals with a predetermined pitch D in the longitudinal direction of the steel pipe, wherein the flat spray nozzles have a spray-water distribution in line symmetry with respect to the center axis of the nozzle and the inclined spray nozzles have a spray-water distribution in line asymmetry with respect to the center axis of the nozzle, the inclined spray nozzles being disposed by being offset by a distance S from the predetermined pitch D, and being tilted with an angle θ of 30° or less, where the angle θ is determined in terms of the relationship θ = arctan(S/H), where S is the distance from the predetermined pitch D of the flat spray nozzles and H is an injection height of the first spray nozzles, wherein the first spray nozzles disposed above the pipe are disposed opposite to each other across the longitudinal direction of the steel pipe lying in the middle, wherein the first spray nozzles disposed above the pipe are disposed opposite to each other with offset of a pitch of D/4 to 3D/4 along the longitudinal direction of the steel pipe, wherein the walking-arm type revolving conveyance apparatus includes a pipe hold-down member that holds down the steel pipe rotating on the rotatable supporting member, and wherein the walking-arm type revolving conveyance apparatus includes second spray nozzles that rapidly cool a region where the first spray nozzles disposed above the pipe interfere with the pipe hold-down member.