Switching schemes have been studied for removing impulse noise. As a switching scheme, pixel-wise median of the absolute deviations from the median (PWMAD) detector was proposed. Since PWMAD detector uses only a single parameter, it is easy to optimize a parameter. However, PWMAD detector can not detect noisy pixels accurately when noisy pixels exist in neighborhood of edge pixels. In this paper, we propose an impulse noise detector using mathematical morphology. We use mathematical morphology in order to improve noise detection in neighborhood of edge pixels. Moreover, the proposed method requires only a single parameter by using mathematical morphology. Carrying out the simulation, we will illustrate the noise detection ratio of the proposed method, and show that it is more accurately to detect noisy pixels than PWMAD detector without increasing parameters.