An arithmetic processing unit included in a pressure change measuring apparatus includes a differential pressure calculation unit configured to obtain a pressure difference between an inner pressure of a cavity and a pressure to be measured based on an output signal of a differential pressure measuring cantilever. A pressure-to-be-measured calculating unit calculates the pressure to be measured based on a set inner pressure of the cavity and the differential pressure calculated by the differential pressure calculation unit. A flow rate calculating unit calculates a flowing quantity of a pressure transmission medium flowing into and out of the cavity for every unit of a predetermined time period based on the differential pressure calculated by the differential pressure calculation unit. An inner pressure updating unit calculates the inner pressure of the cavity after the predetermined time period based on the flowing quantity calculated by the flow rate calculating unit and a volume of the cavity, and updates, to the calculated inner pressure, a set value of the inner pressure of the cavity to be used by the pressure-to-be-measured calculating unit.