A magnetic field measuring apparatus for precise cancellation of environmental noise includes a plurality of first SQUID gradiometers to detect noise and biomagnetic fields, a plurality of second SQUID gradiometers to detect noise, a driving circuit to drive these gradiometers, and a computer to execute signal processing after collecting the signals detected by these gradiometers. First and second SQUID gradiometers are provided which include first-order gradient pickup coils with the baselines formed by the coils of second gradiometers being shorter than those of first gradiometers. The apparatus cancels noise, from detected biomagnetic signal waveforms, caused by variant noise cancellation rates of the coils of first gradiometers, different baselines of the coils of second gradiometers, and the frequency property of a magnetically shielded room in which the apparatus is installed.