This invention relates to a printhead element substrate having a plurality of electrothermal transducers and a plurality of switching elements which drive the plurality of electrothermal transducers. The element substrate has a level converter which is shared by adjacent electrothermal transducers and steps up an input driving signal, and a switch circuit which supplies the driving signal output from the level converter to one of the adjacent electrothermal transducers. The switch circuit switches the supply destination of the driving signal in accordance with an external input selection signal.