A sensor apparatus includes: an element substrate; a detecting section disposed on an upper surface of the element substrate, the detecting section including a reaction section having an immobilization film to detect an analyte; a first IDT electrode configured to generate an acoustic wave which propagates toward the reaction section, and a second IDT electrode configured to receive the acoustic wave which has passed through the reaction section; and a protective film located on the upper surface of the element substrate so as to cover the first IDT electrode, the second IDT electrode, and at least part of the immobilization film, the protective film extending between and contacting with the immobilization film and at least one of the first IDT electrode and the second IDT electrode.