A magnetic field measuring apparatus includes a first processor, a second processor, a motion sensor and a magnetic field sensor. The second processor has higher processing capability than the first processor. The first processor makes the second processor perform certain processing. When it is determined that the state of motion measured by the motion sensor is at a predetermined level or more, the second processor performs a magnetic field correction setting operation as one of the certain processing. The magnetic field correction setting operation involves retrieving measurement values of magnetic field from the magnetic field sensor which are measured at different postures according to a change of the state of motion, and determining an offset correction value for the geomagnetic field based on the measurement values.