Light emitted from a light source module and introduced to an optical fiber is detected with a photodetector. An amplification unit amplifies an output from the photodetector. Using a piezoactuator, the light source module is subjected to reciprocal scanning by repeating one-dimensionally in the X axis direction. In this way, one-dimensional optical intensity distribution in the X-axis direction is obtained based on an output of an amplification unit obtained in accordance with the reciprocal scanning. Based on the one-dimensional optical intensity distribution in the X-axis direction, relative positions between the light source module and the optical fiber are adjusted.