Microwave oven including a cavity for placing food therein, a magnetron for generating a microwave, a waveguide having at least two slots for guiding the microwave from the magnetron to an inside of the cavity, and a stirrer fan rotatably mounted on an inside of the cavity for varying an interfered state of the microwaves periodically, thereby heating the food more uniformly. In one embodiment, the integrating amplifier comprises an input stage including an inverting input coupled to an electrode of a capacitor to sense a capacitance and a non-inverting input coupled to a reference potential, and an output stage including a compensating capacitor coupled to an output. Preferably, the specific gravity Gc is smaller than the specific gravity Gf and smaller than the specific gravity Gs, and the main frame is made of a metal material. The expanded instruction code is embedded in an object program, thus creating and outputting an object program.