A cooking apparatus includes a body, an inner case disposed inside the body in a cooking compartment where food is being cooked, a detection hole formed at a wall of one side of the inner case, so that an infrared ray generated at the cooking compartment is released to the outside of the cooking compartment, and an infrared ray detecting apparatus including a reflecting mirror, which has a plurality of reflection surfaces and configured to change a path of an incident infrared ray, and an infrared ray sensor configured to receive the infrared ray having the path thereof changed to detect an intensity of the infrared ray, thereby reducing the size of a detection hole configured to pass the infrared ray that is generated inside the cooking compartment, so that the adverse effect caused by the leakage of a microwave is minimized.