1. A driving assistance system for a vehicle, the system comprising: a map storage device for storing map data including information items relating to spots including at least one of a facility, a site, and a road; a current position detector for detecting a current position of the vehicle using the stored map data; an executing unit for executing a driving assistance application for a control target in the vehicle using map data on proximity of the detected current position of the vehicle; and a map reliability degree computing unit for computing a map reliability degree, which indicates an accuracy of the map data on proximity of the detected current position with respect to an information item relating to a spot included in the proximity, wherein the executing unit executes the driving assistance application based on an operation associated with the computed map reliability degree, the map reliability computing unit computes a map reliability degree based on, with respect to the spot, (i) positioning accuracy information indicating a positioning accuracy of the map data, (ii) time-based change information indicating a time-based change of the map data from a latest map update, (iii) information accuracy indicating an accordance ratio of the map data relative to actual data with respect to the information item.