There is provided a method of initializing a recording medium having a first surface and a second surface which face to each other with a recording layer in between. The method includes forming interference patterns to have a pitch wider than λr/2N by applying initializing light of a plane wave with a wavelength λf to the recording layer from both of the first surface side and the second surface side, where λr is a wavelength of reproducing light applied to the recording layer at the time of reproducing recorded information, and N is an average refractive index of the recording layer.