A shear punching die assembly having first and second die units (10, 20) in which a material (M) is punched to form a work while the material is clamped between the first and second die units (10, 20)is taught that preferably include a main punch (13) contained in the first die unit and having a cross-sectional shape corresponding to a shape of the work, an ejector (23) contained in the second die unit (20) and positioned axially opposite to the main punch (13), an ejector biasing member (24) normally biasing the ejector (23) toward the main punch (13), an ejector retaining device (42, 50) that is capable of acting on the ejector (23) when the first and second die units (10, 20) are in a closed condition, thereby retaining the ejector (23) in a predetermined position, and an ejector releasing device that is capable of acting on the ejector retaining device (42, 50); when the first and second die units are opened over a desired distance, thereby releasing the ejector (23).