The method is for determining an exposure control value for controlling exposure of a camera mounted on a vehicle to take images in the vicinity of the vehicle. The method includes a detection step of detecting a target from a taken image which the camera has taken in a state where the target is disposed within a image-taking area of the camera, a measurement step of measuring brightness of the target in the taken image, and a calculation step of calculating the exposure control value to such a value that the brightness of the target becomes equal to a target brightness appropriate for recognizing the target.