To provide a power supply device for bioinstrumentation which casts only a little burden on a living body and has a few influence on a small organism such as a fish.

A power supply device is constituted of induction coils 121-128 and a power controller 4, which are installed at the power supply 10 side, and a pickup coil 18 and a power detector 20, which are installed at the sensor 16 side. With power (a) being supplied from the power supply 10, the induction coils 121-128 generate alternating magnetic fields in different directions. The pickup coil 18 generates powerdue to the alternating magnetic fields generated by the induction coils 121-128. The power detector 20 outputs a power signal (c) suited to the magnitude of received power to the space. Based on the power signal (c), the power controller 14 switches the induction coils 121-128 and lets the selected ones generate the alternating magnetic fields so that the received power may be a specified level or above.