1. A Josephson quantum computing device, characterized in that it comprises: a superconducting ring member having a first and a second 0-junction and a π-junction each of which is constituted of a Josephson junction; and a quantum state detecting member constituted by a superconducting quantum interference device arranged outside of said superconducting ring member, wherein: a bonding and an antibonding state brought about by a tunneling effect between a |↑> and a |↓> state as two states degenerate in energy of said superconducting ring member are regarded as quantum bits, and said bonding and antibonding states as the quantum bits are read out by said quantum state detecting member.