A printed board has a board, an electrically insulative membrane, formed on the board, and an electrically conductive membrane, formed on the electrically insulative membrane, in its area where a control circuit, including a CPU and etc., is installed. The electrically conductive membrane is electrically connected with ground patterns of a wiring pattern. Accordingly, ground connections at the control circuit are sufficiently performed. Therefore, even though ground connections in an area other than the control circuit are not sufficiently performed, a magnetic noise is prevented from being generated in a loop-shaped electricity supply line passing through a CPU and etc. Consequently, noises in printed board can be effectively reduced.