The dynamic gain equalizer for flattening a gain profile of an optical amplifier includes: an optical waveguide circuit having multistage optical couplers, demultiplexing and multiplexing, each formed by connecting optical couplers arranged at a plurality of stages; and optical connecting circuits including optical phase shifters each capable of changing a phase of propagating light and optical delay lines each for adding a predetermined delay time to the propagating light, said dynamic gain equalizer in which at least one of the optical couplers in the two multistage optical couplers are provided with variable optical amplitude means, respectively, and each of the multistage optical couplers are formed asymmetrically with respect to an extension of a line which connects a center arranged position of optical outputting ends of the demultiplexing multistage optical coupler with a center arranged position of optical inputting ends of the multiplexing multistage optical coupler.