Disclosed are an optical coupler type filter, and a wavelength stabilizing apparatus of a light source using the same. The wavelength stabilizing apparatus includes an optical coupler type filter including a first waveguide provided with first and second terminals, a second waveguide provided with a third terminal, a coupling region where the first and second waveguides are adjacent to each other so as to couple lights, and a grating disposed in the coupling region, a light source for outputting light to the first terminal, a first optical detector for detecting extracted light outputted from the third terminal as a first electric signal, a signal processor for determining the wavelength of the light outputted from the light source based on the power of the first electric signal, and outputting a control signal in the case that the wavelength of the light deviates from a stabilizing wavelength, and a driver for controlling the output wavelength of the light source based on the control signal, wherein the length of a sub-region of the coupling region, formed between the grating and the first terminal is set to minimize the power of a recurrent light reflected by the grating and outputted to the first terminal.