A route searching device according to an embodiment of the invention includes an estimated fuel consumption amount computing unit that computes an estimated fuel consumption amount of each interval constituting plural routes from a departure point to a destination and an optimum route selecting unit that selects a route in which a total of the estimated fuel consumption amount from the departure point to the destination is minimized. The estimated fuel consumption amount computing unit includes a cruise fuel consumption amount computing unit that computes a cruise fuel consumption amount for each interval by multiplying a distance of the interval and a fuel consumption rate determined according to an average vehicle speed a vehicle-speed fluctuation fuel consumption amount computing unit that computes a vehicle-speed fluctuation fuel consumption amount for each interval in each road category by multiplying the distance of the interval and the a fuel consumption rate, the fuel consumption rate being determined from an average vehicle speed and the road category of the interval and a gradient fuel consumption amount computing unit that computes a gradient fuel consumption amount for each interval by multiplying the distance of the interval and a fuel consumption rate determined according to a road average gradient. The estimated fuel consumption amount is obtained by adding the cruise fuel consumption amount, the gradient fuel consumption amount, and the vehicle-speed fluctuation fuel consumption amount.