A belt meandering preventing device for a running test comprising drum rocking means, the belt meandering preventing device being provided in the running test device that is adapted to evaluate a running characteristic of a rolling element while the rolling element is in contact with a belt laid between a pair of drums (4,5) and correcting meandering of the belt by the drum rocking means that rocks, relative to one of the drums, the other drum about a rocking axis that extends in a vertical direction and that is perpendicular to the rotation axis of the other drum and that changes a position of the belt in accordance with an amount of rocking of the other drum, the amount of rocking being either a rocking angle or a rocking angular velocity of the other drum, the belt meandering preventing device comprising: first control means that is adapted to receive from a third control means a detected position of the belt and control the drum rocking means so that a difference between the received detected position of the belt and a predetermined target position becomes zero; the device being characterised by: second control means that is adapted to detect the amount of rocking of the other drum rocked by the drum rocking means and control the drum rocking means so that the detected amount of rocking of the other drum becomes equal to the target amount of rocking as determined by the first control means; and third control means that is adapted to calculate a difference between an estimated position of the belt obtained by inputting the amount of rocking of the other drum detected by the second control means to a belt response model and a measured position of the belt detected by belt-position detecting means and adapted to calculate an integral obtained by integrating the amount of rocking of the other drum, and adapted to calculate a detected position of the belt on the basis of the sum of the said difference and the integral value, and adapted to input this detected position of the belt to the first control means. first control means that is adapted to receive from a third control means a detected position of the belt and control the drum rocking means so that a difference between the received detected position of the belt and a predetermined target position becomes zero; the device being characterised by: second control means that is adapted to detect the amount of rocking of the other drum rocked by the drum rocking means and control the drum rocking means so that the detected amount of rocking of the other drum becomes equal to the target amount of rocking as determined by the first control means; and third control means that is adapted to calculate a difference between an estimated position of the belt obtained by inputting the amount of rocking of the other drum detected by the second control means to a belt response model and a measured position of the belt detected by belt-position detecting means and adapted to calculate an integral obtained by integrating the amount of rocking of the other drum, and adapted to calculate a detected position of the belt on the basis of the sum of the said difference and the integral value, and adapted to input this detected position of the belt to the first control means. second control means that is adapted to detect the amount of rocking of the other drum rocked by the drum rocking means and control the drum rocking means so that the detected amount of rocking of the other drum becomes equal to the target amount of rocking as determined by the first control means; and third control means that is adapted to calculate a difference between an estimated position of the belt obtained by inputting the amount of rocking of the other drum detected by the second control means to a belt response model and a measured position of the belt detected by belt-position detecting means and adapted to calculate an integral obtained by integrating the amount of rocking of the other drum, and adapted to calculate a detected position of the belt on the basis of the sum of the said difference and the integral value, and adapted to input this detected position of the belt to the first control means.