A light modulation element constituted by a substrate type optical waveguide has a Mach-Zehnder interferometer; and a traveling wave electrode having a signal electrode arranged at least between a first phase modulator and a second phase modulator and electrically connected to both of the first phase modulator and the second phase modulator. A polarity of a semiconductor region of the first phase modulator connected to the signal electrode and a plurality of a semiconductor region of the second phase modulator connected to the signal electrode are different from each other.