An optical module includes: a driver; an optical modulator; a connector that is electrically connected to either the driver or the optical modulator and is provided with an input/output terminal; and a flexible substrate that has flexibility, is connected to the connector, and transfers an electrical signal generated by the driver to the optical modulator, wherein in an end part connected to the connector, the flexible substrate has, on a first surface facing the input/output terminal, a signal-purpose wiring pattern used for transferring the electrical signal and a ground-purpose wiring pattern formed along the signal-purpose wiring pattern, and has, on a second surface that is different from the first surface, a ground electrode that partially covers the second surface and has a shorter electrical distance to the signal-purpose wiring pattern than an electrical distance between the signal-purpose wiring pattern and the ground-purpose wiring pattern.