PURPOSE: To make simple execution of field verification of a curve of transfer to a fixed speed by an experiment at a relatively low speed, by detecting a tension of a tractive rope by a load detector which is provided at couping members of a truck holding the tractive rope and a truck drawing a vehicle for verification.

CONSTITUTION: A truck 1 is drawn by taking up a tractive rope 2 by a drive motor, a vehicle 8 for verification is drawn through the intermediary of coupling members 12, a truck 2 and a rope member 7 and acceleration is made along a rise curve set beforehand and at a prescribed acceleration. At this time, the speed of a take-up drum is detected at two points, i.e., a starting point or a point near the starting point at which the speed of the vehicle C (current value) is very low and a point in a relatively low speed region in which acceleration is made with a prescribed current value, and a tractive force which the drive motor needs to give is estimated. Then, the difference in the tractive force which causes the motions of elongation and contraction of the rope 2 is reproduced by using a curve of transfer to a fixed speed which is stored beforehand, an output of a load detector 11 at that time is once stored 13 and a waveform thereof is made to be drawn after running. Thereby the effectiveness of the curse of transfer to the fixed speed can be judged irrespective of an actual speed of the vehicle 8.