A pressure sensor 1 according to the first aspect of the invention includes: a substrate 50; and a functional element 40 which is laid on the substrate 50 and is composed of functional titanium oxide including crystal grains of at least one of β-phase trititanium pentoxide (β-Ti3O5) and λ-phase trititanium pentoxide (λ-Ti3O5) and having the property that at least a portion of crystal grains of at least one of β-phase trititanium pentoxide (β-Ti3O5) and λ-phase trititanium pentoxide (λ-Ti3O5) change into crystal grains of titanium dioxide (TiO2) when the functional titanium oxide is heated to 350° C. or higher. The substrate 50 includes a substrate thin-film section 51 having a thin film form in which the thickness in the stacking direction of the substrate 50 and the functional element 40 is smaller than that in the other directions.