A method for measuring optical characteristics of a Mach-Zehnder type optical modulation device having an incident part, a waveguide for propagating light incident from the incident part, and a plurality of emitting parts each for emitting light. The method includes inputting light from a light source to the incident part of the optical modulation device through a first optical fiber, receiving emitted lights emitted from the plurality of emitting parts of the optical modulation device by a plurality of light receivers, obtaining a total value of currents by converting electric signals into currents and summing the currents, the electric signals being outputted by the plurality of light receivers receiving the emitted lights, and aligning the incident part of the optical modulation device and the first optical fiber based on the total value of currents.