Abstract: A gas sensor apparatus (1) includes a gas sensor (10) which outputs an output value corresponding to the concentration of a specific gas component contained in a gas; a pressure sensor (20) which measures the pressure of the gas; and a computation section (30) which computes a value representing the concentration of the specific gas component based on the output value from the gas sensor (10) and the pressure of the gas. The computation section (30) computes a concentration value using an expression derived from Fick's law and is a function of the output value and the pressure value, computes a correction value on the basis of a correction term which is a function of the provisional specific-component concentration and the pressure value, and corrects the provisional specific-component concentration using the correction value in order to compute the concentration value of the specific gas component.