In fusion-splicing a dispersion compensating optical fiber having a negative dispersion slope, with a connection optical fiber having a different near field pattern from that of the dispersion compensating optical fiber, if for the connection optical fiber, one is selected such that a theoretical joint loss in a used wavelength, obtained from an overlap integral of a near field pattern of the dispersion compensating optical fiber after fusion splicing and a near field pattern of the connection optical fiber after fusion splicing is presumed to be 0.3 dB or less, in an unconnected state, a construction enabling connection at a low loss results.