A navigation device includes a processing unit electrically connected to a positioning unit and a communication unit. The positioning unit determines a current location of the navigation device and provides corresponding positioning information. The communication unit receives real-time information. The processing unit uses the real-time information and information about a waypoint as a basis to generate a safety speed range, and uses a navigation route and the positioning information as a basis to determine whether a distance between the navigation device and the waypoint is smaller than a preset distance range. If yes, the processing unit provides a speed limit message based on the safety speed range. A navigation device control method as well as a program-storing computer-readable storage medium and a computer program product enabling implementation of the control method are also disclosed.