Provided is an optical control device including first and second optical waveguides, a first control signal electrode including a first input-side signal electrode, a second control signal electrode including a second input-side signal electrode, an inter-signal-electrode ground electrode, a first ground electrode, and a second ground electrode. The substrate has a first groove that is provided between the first input-side signal electrode and the inter-signal-electrode ground, a second groove that is provided between the first input-side signal electrode and the first ground electrode, a third groove that is provided between the second input-side signal electrode and the inter-signal-electrode ground electrode, and a fourth groove that is provided between the second input-side signal electrode and the second ground electrode.