To liquidize the whole of solidified animal/vegetable oil and fat in a short heating time by efficiently heating it by microwave irradiation.

A box-shaped applicator 1 comprising a metallic plate, having an opening and closing door 2 which can be freely opened and closed on its front surface, and having a plurality of open windows 4, 9 formed by arranging them in one direction on each of its bottom surface and back surface, a magnetron 5 to radiate a microwave into the applicator 1 with a wave guide 6 coupled to the applicator by making its coupling windows 7 face a plurality of open windows 4 formed on the bottom surface of the applicator 1, and a magnetron 10 to radiate the microwave into the applicator 1 with a wave guide 11 coupled to the applicator by making its coupling windows 12 face a plurality of open windows 9 formed on the back surface of the applicator 1 are provided. Thereby, since the bottom surface part of the solidified animal/vegetable oil and fat stored in the applicator is heated and melted by microwave radiation by the magnetron 5, and its side part is heated and melted by microwave radiation by the magnetron 10, the whole of it can be melted and liquidized in a short heating time.