Disclosed herein are a magnetometer which is capable of calculating an isotropic magnetic field component by use of three orthogonal coil sensors for magnetic field measurement and a method for measuring a magnetic field using the magnetometer, which records and displays the strength and/or direction of the magnetic field together with the measurement time and position of the magnetic field. The magnetometer can make a more comprehensive understanding of a magnetic field environment and to make a more accurate measurement of a magnetic field. In addition, the magnetometer can reduce time for measurement and result analysis, and obtain reliable measurement results.