PURPOSE: To make the use of an inexpensive speed control device possible without making the function of the control device complicated and highly-developed, by determining the estimated amount of elongation of a tractive rope and by determining a curve of transfer to a fixed speed in consideration of this amount.

CONSTITUTION: The weight of a vehicle C to be tested is set and acceleration is started along a rise curve SL set beforehand and at a prescribed rate. At this time, a running resistance function of a whole system is determined on the basis of speeds and running resistances at the time points when the vehicle/C starts from a starting point or passes a point tp1 near the starting point at which the speed of the vehicle and a current value are very low and when it passes a point tp2 in a relatively low speed region in which the rise curve SL ends and the acceleration is made at a prescribed acceleration. Meanwhile, the amount of elongation of a tractive rope at the time when the vehicle passes the point tp2 is detected by comparing the length of the rope taken up during the time when the vehicle runs between the points tp1 and tp2 with a real distance, and the amount of elongation of the rope just before the entry into a curve of transfer to a fixed speed is estimated by adding the estimated amount of increase of elongation after the detection to the detected amount. By this method, vibration of the tractive rope can be reduced to the minimum and an optimum curve of transfer to the fixed speed which makes transfer possible to a target speed in a short time can be determined.