A semiconductor optical element and an optical module in which extinction ratio variation among integrated optical modulation elements is reduced. The control unit determines whether a failure has occurred in the internal-air-temperature sensor and the external air temperature sensor respectively. The control module is communicatively coupled to the illumination device and the display unit, for sending a first signal to the display unit for displaying the traffic information, and sending a second signal to the illumination device to increase illumination brightness of the illumination device. The second nitride semiconductor layer contains In and includes a first region having a refractive index lower than that of the first nitride semiconductor layer, and a second region having a refractive index lower than that of the first nitride semiconductor layer and an In concentration lower than that of the first region.