A pressure sensor including: a MEMS resonator; a sweeping unit which sweeps a frequency of an excitation signal in a predetermined direction of sweeping, over a predetermined frequency range including a resonance frequency f0 of a vibrator in the MEMS resonator, while outputting the excitation signal to the MEMS resonator; an integrating unit which inputs a vibrating-state information signal as a characteristic amount indicative of a vibrating state of the vibrator from the MEMS resonator while the sweeping unit sweeps the frequency, integrates a plurality of the vibrating-state information signals at different frequencies of the excitation signal, and outputs the integrated value; and a conversion unit adapted to determine a pressure acting on the MEMS resonator, based on the integrated value.