Print element substrate, printhead, and printing apparatus

This invention is directed to a print element substrate including a plurality of print element arrays in which different numbers of print elements are arranged. The print element substrate can efficiently transfer data to each print element and efficiently lay out circuits. The print element substrate includes the following arrangement. More specifically, a first print element array having a relatively large number of print elements, and a plurality of second print element arrays which are equal in length to the first print element array and smaller in the number of print elements than the first print element array are juxtaposed. The print element substrate includes one shift register which holds data for driving the print elements of the first print element array, and one shift register which holds data for driving the print elements of the second print element arrays.