A user inputs a travel distance after last charging of a storage battery of a vehicle into an input field. A capacity of the storage battery at a current charge starting point in time is estimated from a capacity of the storage battery at a last charge ending point in time stored at the last charging and the input travel distance. The estimated capacity of the storage battery is displayed in a display field. During charging of the storage battery, detecting charge current and voltage to estimate a current capacity of the storage battery during charging, a remaining charging period of time and a distance-to-empty by the current capacity and displaying the estimated current capacity, remaining charging period of time and distance-to-empty in display fields are repeated.