A fuel state sensing device is applied to an injector injecting fuel, which is supplied from a fuel pump, though an injection hole. The fuel state sensing device has a fuel pressure sensor (bulk modulus sensing section) for sensing a bulk modulus of the fuel existing in a fuel passage extending from a discharge port of the fuel pump to the injection hole. The fuel state sensing device has a fuel temperature sensor (fuel temperature sensing section) for sensing fuel temperature. The fuel state sensing device has an air mixing state calculating section for calculating a quantity or a ratio of air mixing in the fuel as an air mixing quantity or an air mixing ratio based on the sensed bulk modulus and the sensed fuel temperature.