A voltage sensing apparatus is provided with an output for a voltage tap point that is useful in representing the voltage on a conductor that passes through the voltage sensing apparatus. The SiN layer may be replaced with a layer of another material having an etching selection ratio with reference to SiO2. When the remarked pixel converted into the multivalued data is determined to be the predetermined gradation TJ, it is determined whether a pixel of the predetermined gradation TJ exists in pixels being adjacent to the remarked pixel.