To provide a steering assist and a spin preventing function in a hydraulic vehicle propulsion device.

A hydraulic propulsion vehicle has a car body provided with a pair of front wheels and a pair of rear wheels. A wheel 18 is connected with a fluid displacement variable motor 12 and the motor 12 is connected with a fluid displacement variable hydraulic pump 10 in fluid. A steering angle sensor 20 for detecting an steering angle of the wheel 18 is arranged adjacently to the wheel 18. A speed sensor 22 for measuring a rotating speed output of the motor 12 is provided on the motor 12. A fluid displacement operating device 24 for setting fluid displacement amount of the motor 12 is provided on the motor 12. A computer control device is connected with the speed sensor 22 via electronic impulse and is connected with the operating device 24 and the steering angle sensor 20 so as to obtain information from these devices. A circuit of the control device compares actual speed of the motor 12 with calculated and expected speed of the motor 12 and reduces fluid displacement amount of the motor 12 exceeding the calculated and expected speed.