A power transmission belt including a belt body made of an elastomer, and a cord made of carbon fibers and provided to be embedded in the belt body and to form a helical pattern having a pitch in a belt width direction, wherein the carbon fibers forming the cord are PAN-based carbon fibers, the carbon fibers have a filament diameter of 4 μm or more to 8 μm or less, characterized in that a total number of filaments of the carbon fibers forming the cord is 12000, the cord is a single twist yarn obtained by twisting a filament bundle of the carbon fibers in one direction, the number of twists of the cord of the single twist yarn per 10 cm length is 6/10 cm, the number of cords per 10 mm belt width is 7/10 mm or more to 9/10 mm or less, and a belt tension T 0.2 per 1 mm belt width at 0.2% of a belt extension rate is 70 N/mm or more, a belt tension T 0.5 per 1 mm belt width at 0.5% of the belt extension rate is 220 N/mm or more, and a ratio of the belt tension T 0.2 to the belt tension T 0.5 is greater than at least 0.38, each of the belt tension T 0.2 and the belt tension T 0.5 being obtained by: wrapping, in a 25°C atmosphere, the power transmission belt around a pair of flat pulleys with a pulley diameter of 95.4 mm in a belt tensile tester such that a belt back face comes into contact with the flat pulleys; recording a relationship between displacement between the pair of flat pulleys and a tension detected via either one of the pair of flat pulleys under a condition that one of the flat pulleys is separated from another one of the flat pulleys at a speed of 50 mm/min; doubling the displacement between the pair of flat pulleys, to calculate a belt extension amount, and dividing the belt extension amount by a belt length of the power transmission belt under a no-load condition, to convert the displacement between the pair of flat pulleys into a belt extension rate; meanwhile dividing the detected tension by 2, to calculate a belt tension, and dividing the belt tension by a belt width of the power transmission belt, to convert the detected tension into a belt tension per 1 mm belt width; and performing zero-point amendment based on a relationship between the belt extension rate and the belt tension so that a point at which the belt tension per 1 mm belt width reaches 50N is a starting point. the carbon fibers forming the cord are PAN-based carbon fibers, the carbon fibers have a filament diameter of 4 μm or more to 8 μm or less, characterized in that a total number of filaments of the carbon fibers forming the cord is 12000, the cord is a single twist yarn obtained by twisting a filament bundle of the carbon fibers in one direction, the number of twists of the cord of the single twist yarn per 10 cm length is 6/10 cm, the number of cords per 10 mm belt width is 7/10 mm or more to 9/10 mm or less, and a belt tension T 0.2 per 1 mm belt width at 0.2% of a belt extension rate is 70 N/mm or more, a belt tension T 0.5 per 1 mm belt width at 0.5% of the belt extension rate is 220 N/mm or more, and a ratio of the belt tension T 0.2 to the belt tension T 0.5 is greater than at least 0.38, each of the belt tension T 0.2 and the belt tension T 0.5 being obtained by: wrapping, in a 25°C atmosphere, the power transmission belt around a pair of flat pulleys with a pulley diameter of 95.4 mm in a belt tensile tester such that a belt back face comes into contact with the flat pulleys; recording a relationship between displacement between the pair of flat pulleys and a tension detected via either one of the pair of flat pulleys under a condition that one of the flat pulleys is separated from another one of the flat pulleys at a speed of 50 mm/min; doubling the displacement between the pair of flat pulleys, to calculate a belt extension amount, and dividing the belt extension amount by a belt length of the power transmission belt under a no-load condition, to convert the displacement between the pair of flat pulleys into a belt extension rate; meanwhile dividing the detected tension by 2, to calculate a belt tension, and dividing the belt tension by a belt width of the power transmission belt, to convert the detected tension into a belt tension per 1 mm belt width; and performing zero-point amendment based on a relationship between the belt extension rate and the belt tension so that a point at which the belt tension per 1 mm belt width reaches 50N is a starting point.