A driving characteristics detector includes: a driving information obtaining element for obtaining driving information, which relates to a driving condition of a vehicle; and a driving characteristics determining element for determining driving characteristics of a driver of the vehicle based on the driving information. The driving information includes vehicle speed relating information, which relates to at least one of a vehicle speed, acceleration and deceleration of the vehicle. A driving unit section is defined as a section from the vehicle starts to go until the vehicle stops. The driving characteristics determining element determines the driving characteristics based on the vehicle speed relating information in each driving unit section.