A quantum gate device includes a first superconducting circuit which resonates at a first resonance frequency, second superconducting circuit which resonates at a second resonance frequency, and connector which connects these circuits. The first superconducting circuit includes a single first Josephson device, second Josephson device group, and first capacitor. The second Josephson device group includes n Josephson devices connected by a line made of a superconductor. The Josephson energy possessed by each of the n Josephson devices is greater than n times that of the first Josephson device. The quantum gate device further includes a magnetic field applier which applies a static magnetic field to the partial superconducting circuit, and an electromagnetic wave irradiator (first electromagnetic wave irradiator) which irradiates the first superconducting circuit and/or second superconducting circuit with an electromagnetic wave having a difference frequency which is equal to the difference between the first and second resonance frequencies.