Helical Belt and Belt Transmission Gear

A helical toothed belt comprising:

• a back portion in which a tension member is buried;
• and
• a plurality of tooth portions which are arranged at a predetermined interval along a belt longitudinal direction on one surface of the back portion and each have inclination with respect to a belt width direction, wherein:
• a surface of the tooth portion and a portion of the one surface of the back portion are formed of a tooth fabric;
• the plurality of tooth portions have a tooth pitch of 2 mm or more and less than 4 mm,
• in a case where the tooth pitch of the plurality of tooth portions is 2 mm or more and less than 3 mm, the back portion has a thickness of 0.4 mm or more and 1.2 mm or less,
• in a case where the tooth pitch of the plurality of tooth portions is 3 mm or more and less than 4 mm, the thickness of the back portion is 0.6 mm or more and 1.8 mm or less;
• and
• the tension member is a twisted cord comprising a high-strength glass fiber or a carbon fiber and having a diameter of 0.2 mm or more and 0.6 mm or less, and the tension member is arranged such that each tension member pitch between adjacent tension member is in a range of 0.45 mm or more and 0.6 mm or less.