To reduce the transmission loss of a fusion-splicing connection part and to automatically control the discharging intensity so that the bending of a core is made small by making a reduction value by which the discharging intensity is reduced from a specific reference value proportional to a measured value of an eccentricity quantity.

The center of the tip of an optical fiber fixed in a V groove of a support base and the center of its core tip are read out by an image processor using a TV camera to read the quantity of eccentricity of the core center with the center of the optical center. An adjustment value α for the discharging intensity is calculated from a function expression including the quantity of eccentricity as a variable and the adjustment value α of the discharging intensity is subtracted from the reference value S of the discharging intensity to calculate the discharging intensity H. With this discharging intensity H (reference value S-adjustment value α), the connection end of the optical fiber is heated by induction. For the purpose, many reference values are stored and fusion splicing conditions are inputted to read out and used a reference value S meeting the conditions out of the stored reference values for this arithmetic operation.