A double-cogged V-belt comprising: an endless cord-embedded portion having a cord embedded therein; a lower cogged portion forming an integral part of the cord-embedded portion on an inner peripheral surface thereof; and an upper cogged portion forming an integral part of the cord-embedded portion on an outer peripheral surface thereof, wherein characterized in that the cord is comprised of twisted polyester fiber yarns of 6000 dtex or more in thickness, has an outer diameter of 0.8 mm to 1.5 mm and is able to have a shrinkage rate of 1.2 % to 2.0 % when subjected to a thermal treatment at 120 °C for an hour, and a rubber composition constituting the lower and upper cogged portions (120, 130), that contains respectively short fibers (121,131), such as meta-aramid fibers, and has a hardness of less than 90 degrees, the amount of short fibers (121,131) is from 15 to 25 parts by mass relative to 100 parts by mass of the rubber composition, the short fibers (121,131) having a tensile modulus of elasticity of 5GPa or more, and being oriented such that their grain direction agrees with a belt width direction, and being mixed with, and dispersed in the rubber composition, the thickness of the lower and upper cogged portions (120, 130) being respectively from 5,0 mm to 8,0 mm and from 1,5 mm to 3,5 mm, such that a rate of change of transmission ratio of 1.0 % or less and a normalized efficiency is -1% or more are obtained, wherein the rate of change of ratio is represented by the equation: Rate of Change of Ratio = N 1 / N 2 N 3 / N 4 − N 1 / N 2 / N 1 / N 2 × 100 where, when the belt is wrapped around a drive pulley and a driven pulley and the drive pulley is rotated at 5000 rpm and a drive torque of 8 Nm for 200 hours, N1 and N2 respectively represent input and output numbers of revolutions immediately after the start of the rotation, and N3 and N4 respectively represent input and output numbers of revolutions when 200 hours passed since the start of the rotation, and the normalized efficiency being represented by the equation: Normalized efficiency = transmission efficiency of the belt − transmission efficiency of a reference belt / transmission efficiency of a reference belt where the reference belt is a double-cogged V-belt of an identical shape using a cord having a thermal shrinkage of 0, and the transmission efficiency is represented by a formula of (N2 × Tr2) / (N1 × Tr1) × 100, where, when the belt is wrapped around a drive pulley and a driven pulley and the drive pulley is rotated at 3000 rpm and a drive torque of 4 Nm, N1 and N2 respectively represent input and output numbers of revolutions and Tr1 and Tr2 respectively represent input and output torques immediately after the start of the rotation. an endless cord-embedded portion having a cord embedded therein; a lower cogged portion forming an integral part of the cord-embedded portion on an inner peripheral surface thereof; and an upper cogged portion forming an integral part of the cord-embedded portion on an outer peripheral surface thereof, wherein characterized in that the cord is comprised of twisted polyester fiber yarns of 6000 dtex or more in thickness, has an outer diameter of 0.8 mm to 1.5 mm and is able to have a shrinkage rate of 1.2 % to 2.0 % when subjected to a thermal treatment at 120 °C for an hour, and a rubber composition constituting the lower and upper cogged portions (120, 130), that contains respectively short fibers (121,131), such as meta-aramid fibers, and has a hardness of less than 90 degrees, the amount of short fibers (121,131) is from 15 to 25 parts by mass relative to 100 parts by mass of the rubber composition, the short fibers (121,131) having a tensile modulus of elasticity of 5GPa or more, and being oriented such that their grain direction agrees with a belt width direction, and being mixed with, and dispersed in the rubber composition, the thickness of the lower and upper cogged portions (120, 130) being respectively from 5,0 mm to 8,0 mm and from 1,5 mm to 3,5 mm, such that a rate of change of transmission ratio of 1.0 % or less and a normalized efficiency is -1% or more are obtained, wherein the rate of change of ratio is represented by the equation: Rate of Change of Ratio = N 1 / N 2 N 3 / N 4 − N 1 / N 2 / N 1 / N 2 × 100 where, when the belt is wrapped around a drive pulley and a driven pulley and the drive pulley is rotated at 5000 rpm and a drive torque of 8 Nm for 200 hours, N1 and N2 respectively represent input and output numbers of revolutions immediately after the start of the rotation, and N3 and N4 respectively represent input and output numbers of revolutions when 200 hours passed since the start of the rotation, and the normalized efficiency being represented by the equation: Normalized efficiency = transmission efficiency of the belt − transmission efficiency of a reference belt / transmission efficiency of a reference belt where the reference belt is a double-cogged V-belt of an identical shape using a cord having a thermal shrinkage of 0, and the transmission efficiency is represented by a formula of (N2 × Tr2) / (N1 × Tr1) × 100, where, when the belt is wrapped around a drive pulley and a driven pulley and the drive pulley is rotated at 3000 rpm and a drive torque of 4 Nm, N1 and N2 respectively represent input and output numbers of revolutions and Tr1 and Tr2 respectively represent input and output torques immediately after the start of the rotation.