An apparatus for diagnosing driving behavior includes a storage unit that stores ideal running information defining a relationship between a vehicle speed and a vehicle position corresponding to a road situation, a generation unit that generates actual running information expressing a relationship between an actual vehicle speed and an actual position when a vehicle passes through a road, a condition identification unit that identifies a matching condition where the degree of correlation of the actual running information with the ideal running information exceeds a predetermined value, and a diagnosis unit that diagnoses a driving behavior of a driver of the vehicle, based on a degree of similarity between the ideal running information and the actual running information under the matching condition identified in the condition identification unit.