1. A traffic sign determination device comprising: an image recognition section which detects a first traffic regulation sign by performing an image recognition process on an image of an area in front of a vehicle picked up by an imaging section provided on the vehicle; a map information acquisition section which, using a position of the vehicle, acquires a road link, including a second traffic regulation sign at the position of the vehicle, from a map data storage section storing map data that includes road link information related to roads constituting a map; and a traffic sign determination section which, when no current first traffic regulation sign is detected on a current road link after turning-right or turning-left of the vehicle, determines a current final traffic regulation sign on the current road link, which is to be notified to an occupant of the vehicle, by use of not only a degree of adequacy of cooperation between previous first and second traffic regulation signs detected and acquired on a previous road link before the turning-right or turning-left of the vehicle, but also previous and current factors acquired on the previous and current road links.