A travel drive system for a work vehicle includes: an HST drive device comprising a hydraulic pump driven by a prime mover and a hydraulic motor connected to the hydraulic pump by a closed circuit; an electric motor driven by using electric power generated by drive of the prime mover; a first drive wheel driven by the HST drive device; a second drive wheel driven by the electric motor; a vehicle speed detector that detects a vehicle speed; and a control unit that distributes output of the prime mover to the HST drive device and to the electric motor such that, as the vehicle speed detected by the vehicle speed detector increases, a proportion of a first power distributed to the HST drive device decreases and a proportion of a second power distributed to the electric motor increases.