Toothed Belt and Belt Transmission Mechanism

A toothed belt comprising:

• a back portion;
• at least one tension member embedded in the back portion;
• a plurality of tooth portions arranged at a predetermined interval along a belt longitudinal direction on one surface of the back portion;
• and
• a tooth cloth covering a surface of the tooth portion and a part of the one surface of the back portion, wherein
• the at least one tension member is a twisted cord comprising a high-strength glass fiber filament,
• a tooth pitch between the tooth portions is 2.0 mm or more and 2.5 mm or less,
• a diameter of the at least one tension member is 0.15 mm or more and less than 0.30 mm,
• a ratio of a thickness of the back portion to a thickness of the toothed belt is 22.0% or more and 38.5% or less,
• the tooth portion is constituted of a rubber composition,
• a hardness of the rubber composition at 23° C. is 73° or more and 83° or less, and
• the tooth portion has a shape where a tooth tip portion and two side surfaces sandwiching the tooth tip portion in the belt longitudinal direction are joined together with one or two or more curved surfaces having a fixed curvature.