A quantum Turing machine constituted using a quantum bit created by localizing a phase difference soliton S between superconducting electrons existing in each of multiple of bands in a ring R0 that includes a ring main body R1 formed of a superconductor, and well-shaped portions W1, W2 formed with a reduced line-width at at least two positions on the ring main body R1, can easily constitute a quantum bit, can surely execute a basic logical operation, has multiple-bit capability and, moreover, can ensure sufficient time for executing a quantum algorithm.