To evenly heat an entire bottom surface of a steel plate for cooking various foods or tray for baking various foods by electromagnetic induction.

The electromagnetic induction heater includes: a bobbin (B) around which a center heating coil (14a) with a small radius of a single electromagnetic induction heating coil (14) is wound; similarly, a support foot (F) for sequentially supporting first and second peripheral heating coils (14b)(14c) with large radii; and a core (15) made of a magnetic body vertically penetrated in the center of the bobbin (B). The core (15) is set so as to allow raising or lowering of the core with respect to the bottom surface of the steel plate for cooking various foods or tray (6) for baking various foods, and a fixed gap (X2) secured between two peripheral heating coils (14b)(14c) adjacent to each other is adjustably set to be widened or narrowed.