A magnetic field measurement apparatus including a magnetic sensor array having magnetic sensor cells capable of detecting magnetic fields in three axial directions arranged in three dimensions, each magnetic sensor cell including a plurality of magnetic sensors that each have a magnetoresistive element and a magnetic flux concentrator arranged at least at one of one end and another end of the magnetoresistive element； AD converters that respectively convert analog detection signals output by the magnetic sensors into digital measurement data； a magnetic field acquiring section that acquires the digital measurement data； a calibration computing section that calibrates the digital measurement data from the magnetic field acquiring section, using at least one of a main-axis sensitivity, cross-axis sensitivities, and an offset； and a gradient magnetic field computing section that calculates a gradient magnetic field using magnetic field measurement data resulting from the calibration of the digital measurement data.
