since , food sealed tightly in a packaged does not permit steam to be released from the food during heating , conventional microwave ovens using a hygrometer cannot identify the type of food , and an automatic heating is therefore impossible . a microwave oven of the present invention includes : a temperature detector for detecting the temperature at the top of the lid of the package of a packaged food ; a first calculating unit for calculating a first parameter representing a degree of rise in the detected temperature during a period of time since the heating is started until a predetermined change in the detected temperature is attained ; a second calculating unit for calculating a second parameter representing a degree of rise in the temperature after the predetermined change in the temperature is attained . a controller judges the amount of food in the packaged food based on the first parameter , and judges the packing state of the packaged food based on the second parameter . based on the judgements , or according to the parameters , the controller selects an appropriate heating mode for the packaged food out of a plurality of heating modes varying in the maximum heating time and in the maximum temperature . the heating unit is controlled by the controller according to the heating mode selected .