A cooker is provided. The cooker includes a casing, a cavity part in the casing and including a cooking chamber to cook food, and an exhaust duct through which exhaust gas is discharged. The exhaust duct includes a first duct part having a lower end communicating with the cooking chamber, a second duct part extending from the other end of the first duct part, the second duct part making a predetermined angle with respect to the first duct part or having a predetermined curvature, and a flow passage extension protruded from a portion of the first duct part or the second duct part in an outward direction. At least a portion of the flow passage extension extends at an angle different from the predetermined angle between the first and second duct parts or the flow passage extension has a curvature different from the predetermined curvature of the second duct part.