To provide a method for deciding road freezing, which reduces misdetermination of freezing or nonfreezing of a road by only using information of a road temperature without adding a sensor thereto.

In the method which decides whether the road is frozen or not, the information representing whether a physical numerical value relating to the road temperature continues for a prescribed period or not is obtained, and a decision of freezing or nonfreezing of the road is made based on the information.