An apparatus and method of compensating for the change of an earth magnetic sensor output according to an attitude (roll and pitch) using an inclinometer in the case of calculating azimuth information using a two-axis earth magnetic sensor is disclosed. The attitude of the earth magnetic sensor module is measured using the inclinometer, and a coordinate conversion matrix for converting a body coordinate system to a horizontal coordinate system is calculated. Z-axis direction virtual earth magnetic data at the present attitude of the earth magnetic sensor module is generated using the output of the two-axis earth magnetic sensor and the calculated attitude information. After the generated Z-axis earth magnetic data and the measured X-axis and Y-axis earth magnetic data are converted into the horizontal coordinate system, the calculated azimuth angle is considered as the azimuth angle of the earth magnetic sensor module.