To easily and quickly mount and demount a top plate to a cabinet of a system kitchen.

A mounting screw 62 is engaged with and fixed to a screw hole 421 of a mounting piece mounted at a rear inner side of a casing 11 for loading a heater main body 12 through a mounting hole 52 formed on a rear end of an upper face of a frame body 32 constituting the top plate 30, at a rear side of the top plate, and the mounting screw 62 is covered by an exhaust cover 33 to be concealed. On the other side, an engagement hole 511 is formed on a retaining piece 51 extended to a lower end of the frame body 32 at a front side of the top plate 30, and an elastic leg part 411 of a plate spring 41 mounted on a front inner side of the casing 11 is fitted in the engagement hole 511 to be retained.