An electric rice cooker is disclosed which has a cooking kettle containing rice and water, a thermal insulating frame and an electric heater provided adjacent to the outside surface of the kettle. The electric rice cooker performs auxiliary cooking, such as "twice cooking", for effectively converting beta-starch to alpha-starch after main cooking is completed. The auxiliary cooking operating time is properly determined in accordance with the actual amount to be cooked when every cooking operation is performed. The actual amount to be cooked is detected by a control circuit arranged in a case in accordance with a change in actual kettle temperature measured by a thermistor after a heater is deenergized, that is, in accordance with a peak temperature obtained by "after heat".