A heating cooker for a microwave oven in which in a main body through which microwaves are transmitted, an upper portion of a metallic pan is closely coupled, and a heating sheet receiving the microwaves and generating heat and an insulating support are coupled in order onto an undersurface of the pan, the heating cooker including a safety device configured such that a silicone packing is provided in a section of the close coupling between the pan and the main body, and so that if internal pressure of the cooker rises abnormally, the silicone packing is decoupled from the main body so as to reduce the pressure.