An imaging device is provided, in which a front sheet metal casing and/or a back sheet metal casing can be secured to a top sheet metal casing without the necessity of providing any screw holes in the top surface of the top sheet metal casing in order to secure the top sheet metal casing to the front sheet metal casing and/or the back sheet metal casing. The top sheet metal casing includes a top plate and a secured sheet metal casing secured to the top plate such that at least a portion of its perimeter is spaced apart from the top plate at a predetermined distance. A flange provided to the front or back sheet metal casing is inserted between the top plate and the secured sheet metal plate, so that an engagement pin provided to the secured sheet metal plate is fitted in an engagement hole provided in the flange, thereby securing the front or back sheet metal casing to the top sheet metal casing.