The present invention provides an elastic force magnifying structure of self-opening/closing umbrella. The umbrella includes a central post that comprises an inner tube, an intermediate tube, and an outer tube telescopically fit to each other. The central post receives a primary spring received therein. The elastic force magnifying structure includes an elastic force increasing spring arranged inside the outer tube. The elastic force increasing spring is coupled by a coupling sleeve to the primary spring to serve as an extension thereof.