A piezoelectric element substrate is provided. The piezoelectric element substrate includes: a substrate member; a plurality of piezoelectric elements on the substrate member; a plurality of wiring patterns on one side of the substrate member on which the plurality of piezoelectric elements is disposed; and a bonding pattern in a region different from the wiring patterns on the one side of the substrate member. Each of the piezoelectric elements includes a first electrode, a piezoelectric body, and a second electrode. The wiring patterns are connected to the corresponding piezoelectric elements. The bonding pattern is to be bonded to another substrate directly or via an insulating film, and is made of a metal layer having a plurality of slots.