Sponge cake premix and method of manufacturing sponge cake by using said premix

The present invention is directed to a sponge cake premix that can be cooked easily with a microwave oven to prepare a sponge cake. A batter prepared by adding a thermocoagulation protein to a sponge cake premix containing as a main ingredient a cereal powder consisting of starch and a pregelatinized starch is cooked under heat with a microwave oven to obtain a sponge cake that permits eliminating the gum-like hard texture inherent in conventional sponge cakes of this type and exhibits a light and soft texture. The obtained sponge cake is free from bake shrinkage and exhibits a good-looking voluminous appearance.