PURPOSE: To improve the transmission characteristic in the connection of an optical fiber having variance in group velocity dispersion.

CONSTITUTION: A mean value <D> of group velocity dispersion values D of plural optical fibers OF1, OF2,..., OFM-1, OFM is obtained and the optical fibers are classified into a 1st optical fiber group whose group velocity dispersion is higher than the mean value <D> and a 2nd optical fiber group whose group velocity dispersion is lower than the mean value <D> and an optical fiber is selected from the two groups sequentially and connected to reduce or minimize a parameter I (Z) according to equation (where Z is a distance in a transmission direction and Z=0 is a start position of the line).