A frequency of input power is selected with a first keypad, and a weight unit is selected with a second keypad provided on a microwave oven. A displaying unit is connected with the key inputting devices and displays operating conditions of the microwave oven that are set by the first and second keypads. A controller detects the operating conditions by checking whether the displaying means and each of the first and second keypads form closed loops by applying control signals to the loops and sets the detected operating conditions as preset operating conditions of the microwave oven. Then, the controller controls the cooking operation of the microwave oven according to the preset conditions.