Disclosed is a technique for calculating Distance to Empty (DTE) in an electric vehicle. In the disclosed technique, a past driving average fuel efficiency is calculated. An air conditioning average energy consumption rate during past driving is calculated. A past driving average fuel efficiency when assuming an air conditioning apparatus is not used from the past driving average fuel efficiency and the air conditioning average energy consumption rate is calculated. A current driving fuel efficiency is calculated. Then the past driving average fuel efficiency when assuming the air conditioning apparatus is not used and the current driving fuel efficiency are blended, and the DTE is calculated from the blended driving fuel efficiency.