PURPOSE: To provide a circuit board which is capable of feeding an electric power to a Josephson device through a polyphase pulsating current power supply system and being mounted with Josephson devices high in density.

CONSTITUTION: A Josephson device mounting circuit board 2 is primarily composed of an insulating board 4 and an insulating layer 5 which includes an inner circuit 60 and is formed on the insulating board 4. An alternating current power supply circuit 9 which feeds two alternating currents different from each other in phase to Josephson devices 3 and a direct current power supply circuit 8 which feeds a direct bias current to the Josephson devices 3 to control timing between the output pluses of two alternating currents are provided inside the insulating board 4. The direct current power supply circuit 8 is composed of circuit patterns provided onto sheets 6a and 6b which constitute the insulating board 4, and an LC filter which restrains an alternating current and a direct bias current from interfering with each other is composed of a capacitance between the circuit patterns and an inductance of the circuit patterns.