A resonant pressure sensor includes a first substrate and a resonator. The first substrate includes a diaphragm and a projection disposed on the diaphragm. The resonator is disposed in the first substrate, a part of the resonator being included in the projection, and the resonator being disposed between a top of the projection and an intermediate level of the first substrate. The first substrate is an SOI substrate in which a silicon dioxide layer is inserted between a silicon substrate and a superficial silicon layer. The intermediate level of the first substrate is disposed in the silicon substrate, and the resonator is disposed in the projection included in the superficial silicon layer.