A work vehicle, comprising: an engine; a hydraulic pump driven by the engine; a work implement driven by hydraulic fluid discharged from the hydraulic pump; a work implement operating member for operating the work implement; a pressure sensor for detecting a hydraulic pressure of the hydraulic pump; a travel device driven by the engine; a power-transmission device (24, 124) configured to transmit driving power from the engine to the travel device; and a vehicle speed detecting unit for detecting a vehicle speed; an accelerator operating member; an accelerator operation detecting unit for detecting an operation amount (Aac) of the accelerator operating member; and a control unit configured to control the power-transmission device (24, 124); wherein, the power-transmission device (24, 124) has: an input shaft; an output shaft; a gear mechanism including a planetary gear mechanism (68, 69, 168), the gear mechanism being configured to transmit rotation of the input shaft to the output shaft; and a motor (M1, M2) connected to a rotating element of the planetary gear mechanisms (68, 69, 168); and, the power-transmission device (24, 124) is configured so that a rotation speed ratio of the output shaft with respect to the input shaft is changed by changing the rotation speed of the motor (M1, M2), and the control unit has: a work implement requirement determination unit for determining a work implement required horsepower (Hpto) on the basis of the operation amount (Aac) of the work implement operating member and the hydraulic pressure of the hydraulic pump; a transmission requirement determination unit for determining a transmission required horsepower (Htm) on the basis of the vehicle speed and the operation amount (Aac) of the accelerator operating member; and an engine requirement determination unit for determining an engine required horsepower (Hdm) on the basis of the work implement required horsepower (Hpto) and the transmission required horsepower (Htm); and a required throttle determination unit for determining a required throttle value (Th_tm1, Th_ac) based on the engine required horsepower (Hdm). an engine; a hydraulic pump driven by the engine; a work implement driven by hydraulic fluid discharged from the hydraulic pump; a work implement operating member for operating the work implement; a pressure sensor for detecting a hydraulic pressure of the hydraulic pump; a travel device driven by the engine; a power-transmission device (24, 124) configured to transmit driving power from the engine to the travel device; and a vehicle speed detecting unit for detecting a vehicle speed; an accelerator operating member; an accelerator operation detecting unit for detecting an operation amount (Aac) of the accelerator operating member; and a control unit configured to control the power-transmission device (24, 124); an input shaft; an output shaft; a gear mechanism including a planetary gear mechanism (68, 69, 168), the gear mechanism being configured to transmit rotation of the input shaft to the output shaft; and a motor (M1, M2) connected to a rotating element of the planetary gear mechanisms (68, 69, 168); and, the power-transmission device (24, 124) is configured so that a rotation speed ratio of the output shaft with respect to the input shaft is changed by changing the rotation speed of the motor (M1, M2), and the control unit has: a work implement requirement determination unit for determining a work implement required horsepower (Hpto) on the basis of the operation amount (Aac) of the work implement operating member and the hydraulic pressure of the hydraulic pump; a transmission requirement determination unit for determining a transmission required horsepower (Htm) on the basis of the vehicle speed and the operation amount (Aac) of the accelerator operating member; and an engine requirement determination unit for determining an engine required horsepower (Hdm) on the basis of the work implement required horsepower (Hpto) and the transmission required horsepower (Htm); and a required throttle determination unit for determining a required throttle value (Th_tm1, Th_ac) based on the engine required horsepower (Hdm). a work implement requirement determination unit for determining a work implement required horsepower (Hpto) on the basis of the operation amount (Aac) of the work implement operating member and the hydraulic pressure of the hydraulic pump; a transmission requirement determination unit for determining a transmission required horsepower (Htm) on the basis of the vehicle speed and the operation amount (Aac) of the accelerator operating member; and an engine requirement determination unit for determining an engine required horsepower (Hdm) on the basis of the work implement required horsepower (Hpto) and the transmission required horsepower (Htm); and a required throttle determination unit for determining a required throttle value (Th_tm1, Th_ac) based on the engine required horsepower (Hdm).