To output a polarization entangled photon pair, using a waveguide non-linear element.

A non-linear waveguide 22 generates signal photons and idler photons from pulse light generated from a pump light source 21, at a prescribed generation efficiency. A polarization modulator 23 modulates the polarization state of the output of the light by the non-linear waveguide 22. A first polarization beam splitter 24a has a polarization separation function, and the light output by the polarization modulator 23 is branched into two optical paths, in response to the polarization state. A second polarization beam splitter 24b has the polarization combining function, and light, branched into the two routes by the first polarization beam splitter 24a, is coupled to the same path. The difference in the light propagation time in the two paths between the first polarization beam splitter 24a and the second polarization beam splitter 24b is set so as to be equal to the time interval of two pieces of continuous pulse light.