The present invention relates to a pressure measuring apparatus, characterized in that: the pressure measuring apparatus comprises a pressure sensor having a first resistor for sensing an external stress and a second resistor acting as a reference, wherein the second resistor is acting as a reference while the first resistor is used for measuring an external stress in that a first oscillating signal received by an end of the first resistor is affected by the external stress, and consequently an affected first oscillating signal varied with respect to the external stress is outputted from the other end of the first resistor, and a second oscillating signal received by an end of the first resistor is outputted from another end of the second resistor without being affected by the external stress. Hence, the present invention provides a pressure measuring apparatus and a pressure sensor thereof using the frequency difference of the oscillating signal in accordance to the variation of the resistor value as base for measuring the external stress. Hence, the present invention requires no amplifier and A/D converter so that the whole manufacturing process is simplified and also the overall cost of the pressure measuring apparatus is reduced.