A vehicle system includes an information processing device and a vehicle. The vehicle includes: a detection unit configured to detect an illuminance change; an acquisition unit configured to acquire position information; a first sending unit configured to send, to the information processing device, (i) illuminance change position information and (ii) traveling information; a first receiving unit configured to receive a turn-on condition from the information processing device; and a turn-on unit configured to turn on a headlight according to the traveling information and the turn-on condition. The information processing device includes a learning unit configured to learn, as the turn-on condition, traveling content of the vehicle before the vehicle reaches the position where the illuminance change is detected, by using the travelling information, and a second sending unit configured to send the turn-on condition to the vehicle.