An object of the present invention is to provide an optical add-drop multiplexer capable of giving improved characteristics with a simple, inexpensive arrangement which needs not a corresponding number of optical bandpass filters to the wavelength components of a light signal to be carried. The wavelength components .lambda.1 to .lambda.n of an input n-wave signal is received by an input optical fiber and transmitted through an optical circulator and an optical fiber to an optical bandpass filter which allows a specific wavelength .lambda.1 to pass but rejects the other wavelengths .lambda.2 to .lambda.n. While the rejected wavelengths .lambda.2 to .lambda.n are returned back to the optical fiber, the specific wavelength .lambda.1 runs through another optical fiber and another optical circulator and then is dropped from an output optical fiber. Meanwhile, another signal component of the wavelength .lambda.1 is added and introduced from another input optical fiber through the another optical circulator and the another optical fiber to the optical bandpass filter. Upon the added wavelength .lambda.1 having passed the optical bandpass filter and entering the optical fiber, it is mixed with the rejected wavelengths .lambda.2 to .lambda.n. A resultant sum signal of the full wavelengths .lambda.1 to .lambda.n is passed through the optical circulator and transmitted from an output optical fiber.