Provided is an optical modulator in which a phenomenon of a resonance mode or the like is prevented from being generated in a recess portion of a housing that mounts a flexible printed circuit and of which broadband characteristics are improved.There is provided an optical modulator in which an optical modulation element is mounted inside a housing, in which at least a portion of an electric line is connected to an external circuit board 7 through a flexible printed circuit 6, and which is disposed on the external circuit board. A recess portion (area indicated with a dotted line D) that mounts the flexible printed circuit is formed on an outer bottom surface of the housing and at a part where the flexible printed circuit is connected, and means for preventing a resonance mode or the like (for example, a corrugated shape 21) is provided such that a resonance mode of a microwave and a millimeter wave or a parallel plate mode is prevented from being generated among a surface A of the recess portion facing the flexible printed circuit, an electric wiring part B provided on the flexible printed circuit overlapping the surface A when seen in a plan view, an electric wiring part C provided on the external circuit board overlapping the surface A when seen in a plan view.