A photon pair generating device capable of further increasing generation efficiency of a correlation photon pair is provided, the photon pair generating device generating the correlation photon pair by a hyper-parametric scattering. A quantum well is provided in a resonator. An incident light radiated from a light source to the resonator resonates therein and becomes a particular resonator mode. The generation efficiency of the correlation photon pair by the hyper-parametric scattering in the quantum well is enhanced by disposing the quantum well in a position where electric field strength of the light becomes higher by this resonator mode.