To detect road surface conditions more accurately.

Reference data in a prescribed section of a contact sound between a tire of a vehicle to be inspected and the road surface, which is a reference for determining whether the road surface is required to be repaved or not, are stored in a reference data storage part 17 corresponding to map information. When the contact sound not including a disturbance sound acquired by removing the component of the disturbance sound from the contact sound including the disturbance sound is provided, a control part 14 calculates the average sound volume thereof, and determines whether the calculated average sound volume is larger than a reference sound volume of the reference data or not. When determining that the measured average sound volume is larger than the reference sound volume of the reference data, the control part 14 recognizes that the road surface in the measurement section is a road surface required to be repaved, and displays warning information to an inspector on a display part 19.