The mechanical relaxation spectrum of crystalline polymers shows a slope less than that of the wedge type in the amorphous region under the influence of the crystalline regions. Further we assume, in a chain that runs through two crystalline regions, the friction constant of the segments in the middle part of the chain is smaller than that of the segments near the crystalline regions. Then it is shown that this heterogenuity in the friction constant makes the slope of the relaxation spectrum a slope slightly less than 1/2. But the agreement with the experiment is yet far.