A multistage Mach-Zehnder interferometer type optical circuit including any number of symmetrical Mach-Zehnder interferometers and any number of asymmetrical Mach-Zehnder interferometers connected in cascade. In the optical circuit, low coherence light is used first to obtain individual phase control conditions of the symmetrical Mach-Zehnder interferometers without being affected by the asymmetrical Mach-Zehnder interferometers. Second, phase control conditions of the individual asymmetrical Mach-Zehnder interferometers are obtained by controlling the symmetrical Mach-Zehnder interferometers based on the first phase control conditions. Finally, the characteristic adjustment of the whole multistage Mach-Zehnder interferometer type optical circuit is carried out by controlling all the interferometers based on the phase control conditions of both the symmetrical Mach-Zehnder interferometers and asymmetrical Mach-Zehnder interferometers and setting the phase shift amounts of the individual interferometers at appropriate values.