The length portion of part of a multiband superconductor line 10 is used as a closed circuit line part Rc that constitutes part of a closed circuit allowing passage of an electric current Io generated by an electric current source 12. Meantime, the line part extending and continuing into the closed circuit line part Rc is used as an open circuit line part Ro adapted to serve as an open circuit regarding the electric current source 12. By keeping the multiband superconductor line 10 under a temperature environment falling short of the critical soliton temperature and injecting a nonequilibrium electric current Io from the electric current source 12 into the closed circuit line part of the multiband superconductor line, it is rendered possible to induce generation of an interband phase different soliton So. The generated interband phase difference soliton So is forwarded as separated from the electric current Io to the open circuit line part Ro and is made to run therein. The open circuit line part Ro is provided with a Josephson junction 15 and consequently enabled to induce extinction of the interband phase different soliton So that has advanced thereto, during which time the voltage generated by the AC Josephson effect is detected with the voltage detecting device 13.