This invention is directed to real time detection of occurrence of a transfer error and feedback of the detection result to a printing apparatus in consideration of a possible risk that a signal transfer error occurs on a transfer path that becomes longer as the printhead is elongated. To accomplish this, in a printhead configured by cascade-connecting a plurality of element substrates, information of a transfer error detected in real time in each element substrate during transfer of a print data signal is output to an element substrate on the next stage by taking account of information input from an element substrate on the preceding stage. Information containing pieces of information from all element substrates is output from an element substrate on the final stage.