a and 18 b at the outside of the inner case 13 at the rear of the cooking chamber 11 is mounted a heater case 21 by which a first upper heater compartment 20 a and a second lower heater compartment 20 b are defined while the first upper heater compartment 20 a and the second lower heater compartment 20 b are divided from each other as shown in fig2 in the first heater compartment 20 a are mounted a first circulating fan 22 a to circulate air inside the first cooking chamber 11 a and a first heater 23 a which is disposed at the outer circumference of the first circulating fan 22 a in the second heater compartment 20 b are mounted a second circulating fan 22 b to circulate air inside the second cooking chamber 1 b and a second heater 23 b which is disposed at the outer circumference of the second circulating fan 22 b at the outside of the heater case 21 b are mounted a first motor 24 a to drive the first circulating fan 22 a and a second motor 24 b to drive the second circulating fan 22 b however the present invention is not limited to any particular number of heaters and may vary as necessary at the rear walls of the first and second cooking chambers 11 a and.