A road surface state determination device includes a tire-side device and a vehicle-body-side system. The tire-side device is attached to a tire of a vehicle. The vehicle-body-side system is included in a vehicle body. The tire-side device outputs a detection signal corresponding to a magnitude of vibration of the tire. The tire-side device generates road surface data indicative of a road surface state shown in a waveform of the detection signal. The tire-side device transmits the road surface data. The vehicle-body-side system receives the road surface data transmitted from the tire-side device. The vehicle-body-side system determines the road surface state of a road surface on which the vehicle is traveling based on the road surface data and learning data.