In this paper, we propose a new tuning method of threshold, which is a parameter of a switching median filter, by using the distribution distance. The switching median filter detects noise-corrupted pixels based on a threshold, and restores only the detected pixels. The present switching median filter deals with the random-valued impulse noises, whose distribution is ideally assumed as a uniform. In the present method, the threshold is tuned by evaluating a distribution distance between the assumed and the detected noises. L₁-norm is used here as the distribution distance. The effectiveness of the proposed method is verified by some experiments.