A SQUID bias current adjustment device (AC SUPPLY) supplies a sinusoidal current at 40 kHz, for example, to a coil (12) to generate magnetic field at a SQUID (10). The amplitude of the field corresponds to a half period of a field-voltage characteristic. Voltage generated from the SQUID at this time is filtered by using a filter (14) to pick out components of 40 kHz and 80 kHz. The picked out signal components are rectified and converted to direct current, and the bias current is adjusted such that the maximum value is obtained. In this way, a SQUID bias current adjustment device can be provided capable of automatically adjusting bias current properly in a short period of time.