An optical cross-connect apparatus that realizes highly efficient optical cross-connection by performing large-scale switching. This optical cross-connect apparatus comprises first wavelength converters for converting m different wavelengths null1 through nullm contained in n WDM input optical signals into 2m wavelengths null1 through null2m; a first wavelength cross-connector for performing cross-connection according to wavelengths, including demultiplexers for separating the optical signals wavelength-converted by the first wavelength converters into 2m wavelengths and multiplexers for combining optical signals with the 2m separated wavelengths, wherein the same wavelengths should not be sent via each of bundles of 2m/n lines by which the demultiplexers and the multiplexers are connected; second wavelength converters for converting the 2m wavelengths contained in the optical signals cross-connected by the first wavelength cross-connector into 2m wavelengths; a second wavelength cross-connector for performing cross-connection according to wavelengths, including demultiplexers for separating the optical signals wavelength-converted by the second wavelength converters into 2m wavelengths and multiplexers for combining optical signals with the 2m separated wavelengths, wherein the same wavelengths should not be sent via each of bundles of 2m/n lines by which the demultiplexers and the multiplexers are connected; and third wavelength converters for converting the 2m wavelengths null1 through null2m contained in the optical signals cross-connected by the second wavelength cross-connector into m wavelengths null1 through nullm and for sending the m wavelengths null1 through nullm.