The present invention relates to a microwave oven. According to the present invention, a fixed heater 41 is installed on a ceiling of a cavity 31 of a microwave oven, and a pivotable heater 43 is installed to pivot upward and downward on its lower end in the cavity 31. When the pivotable heater 43 has been pivoted downward on its lower end, a grill 45 on which an object to be heated is seated is horizontally installed between a lower surface of the fixed heater 41 and an upper surface of the pivotable heater 43. A micro-switch 51, which will be pushed by the grill 45 and thus generate an actuating signal for pivoting the pivotable heater 43, is installed on a side surface of the cavity 31. According to the present invention, since the fixed and pivotable heaters 41 and 43 heat upper and lower surfaces of the object, respectively, and the pivotable heater 43 is pivoted according to whether the grill 45 is mounted or detached, it is possible to cook the object faster and more conveniently.