PURPOSE: To provide a high-output and nondeflecting variable wavelength light source by amplifying a light narrow in wavelength band area, which has permeated a variable wavelength filter from an end face emission type light emitting diode module, using an Er-added optical fiber and a laser diode module for excitation.

CONSTITUTION: This light source is of such constitution that an end face emission type light emitting diode module 1 and a variable wavelength filter 7 are connected with each other, that the output end of the variable wavelength filter 7 and a laser diode module 2 for excitation are connected to the respective input ports of the photosynthetic wave divider 4, and that an Er-added fiber 3 is connected to the output port of the photosynthetic wave divider 4.