Toothed belt

A transmission system using a toothed belt, the transmission system comprising:

• a toothed belt including a belt body made of elastomer and a core wire made of carbon fiber and provided so as to be embedded in the belt body and form a helix having a pitch in a belt width direction;
• and
• a toothed pulley meshed with the toothed belt, wherein
• the belt body includes a flat band portion having a horizontally long rectangular cross section and a plurality of tooth portions integrally provided on an inner peripheral side of the flat band portion,
• the core wire is a single twisted yarn formed by twisting a filament bundle of carbon fiber forming the core wire in one direction,
• a number of twists of the core wire of the single twisted yarn per length of 10 cm is four times/10 cm or more and twelve times/10 cm or less, and
• a belt tension T0.2 per belt width of 1 mm when a belt elongation rate is 0.2% is 70 N/mm or more, an amount of backlash between the toothed belt and a toothed pulley is 0.10 mm or more and less than 0.65 mm, a hardness of the belt body is 89° or more in JIS K 6253 Durometer Type A, and a surface dynamic friction coefficient is 1.5 or less.