A gas concentration measuring apparatus is provided which works to calculate the concentration of a given gas component with enhanced accuracy. The gas concentration measuring apparatus 1 includes, a gas sensor 10 and a calculating portion 11. The gas sensor 10 is equipped with a pump cell 3, a monitor cell 4, and a sensor cell 5. The calculating portion 11 subtracts a monitor cell current Im that is a current flowing through the monitor cell 4 from a sensor cell current Is that is a current flowing through the sensor cell 5 to calculate the concentration of the given gas component in gas g. When calculating the concentration of the given gas component, the calculating portion 11 performs a correction operation to bring a value of the monitor cell current Im close to a value of an oxygen dependent current Iso that is a component of the sensor cell current Is which arises from the concentration of oxygen.