If we zoom in a certain part of the Mandelbrot set, we　can see a figure J' which is very similar to a certain　Julia set. Furthermore, as we zoom in the middle part of J', we can see a certain nested structure which is
similar to the iterated preimages of J' by z^2 and finally　a small Mandelbrot set M' appears. We explain how to formulate this phenomena and show that this actually occurs. Also we show that this kind of nested structure exists in J_c for c in M'.