In a device to detect a drive country in which a subject vehicle is located, a control section acquires correspondence information which shows a relationship between traffic signs and a degree of installation reliability of a traffic sign in each country as a drive country candidate in which the subject vehicle is located. The degree of installation reliability of each traffic sign indicates a degree of installation reliability located in each country. The control section acquires matching information which represents whether a traffic sign located around the subject vehicle matches the traffic sign stored in the correspondence information. The control section reads the degree of installation reliability of the traffic sign indicated by the matching information in each country stored in the correspondence information, and estimates, as the drive country in which the subject vehicle is driving, the country having a maximum degree of installation reliability of the traffic sign read from the correspondence information.