A cooker is provided. The cooker includes a casing defining an exterior of the cooker, a cavity part disposed in the casing, the cavity part including a cooking chamber having an interior to receive food, a burner disposed in the cooking chamber to burn a mixture gas of air and gas so as to supply energy to the interior of the cooking chamber, a compartment member dividing the interior of the cooking chamber into a food cooking region and a gas mixing region where air and gas are supplied to form a mixture gas, and a door configured to selectively close or open the cooking chamber.