A driving circuit layout can suppress an increase in the area of a head substrate in an inkjet printhead adopting a constant electric current driving method. A plurality of printing elements and a plurality of switching elements which are very large in number are arrayed in the longitudinal direction of a head substrate. A terminal which receives a driving signal and a control signal that are used to drive the plurality of printing elements is arranged at the end of the board in the widthwise direction of the board. An electric current source for supplying a predetermined electric current is interposed in an area between these two areas.