An IQ optical modulator, comprising: a parent Mach-Zehnder type optical waveguide functioning as a parent; child MZM optical waveguides functioning as a child that constitute two arms of the parent MZM optical waveguide; two electrode transmission lines that are provided along two arms of the child MZM optical waveguides, respectively, and that receive a modulation signal to thereby phase-modulate an optical signal propagating in the child MZM optical waveguides; an RF extension line that is connected to the two electrode transmission lines, respectively, and that is used to input the modulation signal applied to the two electrode transmission lines; a first optical splitter for branching light into the two arms of the parent MZM optical waveguide; second optical splitters for branching light into the two arms of the child MZM optical waveguides; and first optical multiplexers for multiplexing light from the two arms of the child MZM optical waveguides, and a second optical multiplexer for multiplexing light from the two arms of the parent MZM optical waveguide, wherein: the child MZM optical waveguides including the two electrode transmission lines have a stripe direction that is: the same as a stripe direction of the RF extension line, a stripe direction of the second optical splitters, and a stripe direction of the first optical multiplexers, and orthogonal to a stripe direction of the first optical splitter characterized in that the stripe direction of the child MZM optical waveguides including the two electrode transmission lines is orthogonal to a stripe direction of the second optical multiplexer. a parent Mach-Zehnder type optical waveguide functioning as a parent; child MZM optical waveguides functioning as a child that constitute two arms of the parent MZM optical waveguide; two electrode transmission lines that are provided along two arms of the child MZM optical waveguides, respectively, and that receive a modulation signal to thereby phase-modulate an optical signal propagating in the child MZM optical waveguides; an RF extension line that is connected to the two electrode transmission lines, respectively, and that is used to input the modulation signal applied to the two electrode transmission lines; a first optical splitter for branching light into the two arms of the parent MZM optical waveguide; second optical splitters for branching light into the two arms of the child MZM optical waveguides; and first optical multiplexers for multiplexing light from the two arms of the child MZM optical waveguides, and a second optical multiplexer for multiplexing light from the two arms of the parent MZM optical waveguide, wherein: the child MZM optical waveguides including the two electrode transmission lines have a stripe direction that is: the same as a stripe direction of the RF extension line, a stripe direction of the second optical splitters, and a stripe direction of the first optical multiplexers, and orthogonal to a stripe direction of the first optical splitter characterized in that the stripe direction of the child MZM optical waveguides including the two electrode transmission lines is orthogonal to a stripe direction of the second optical multiplexer. the same as a stripe direction of the RF extension line, a stripe direction of the second optical splitters, and a stripe direction of the first optical multiplexers, and orthogonal to a stripe direction of the first optical splitter characterized in that the stripe direction of the child MZM optical waveguides including the two electrode transmission lines is orthogonal to a stripe direction of the second optical multiplexer.