Presented is a mathematical model of single-product economy describing a nominal economic growth and a nominal economic decline. Based on the model of economic dynamics, policies handling the gravity of the secular stagnation are furnished. First, transition of the secular stagnation into the secular decline is to be prevented. Second, a two-stage economic policy against the secular stagnation should be entertained. The first stage is to promote a policy of advancing the additional demand for products to counterbalance the additional supply of products by external suppliers. The second stage is to sustain a policy of savings and investments to stipulate an economic growth where the savings and investments are to be committed with a modest acceleration. Two stages of the alleviating economic policy can be executed concurrently.