To display the residual capacity and the failure diagnosis of a battery clearly for, for example, a user or a salesperson who is not experienced in an electrically assisted vehicle.

A display has a battery residual capacity calculation part 1 for calculating the residual capacity of a battery based on the battery voltage of an auxiliary power and the current value of the auxiliary power and a residual capacity display pattern specification part 4 for specifying the residual capacity display pattern based on the residual capacity of the battery that is calculated by the battery residual capacity calculation part 1, and a display part 6 for displaying the residual capacity of the battery based on the display pattern that is specified by the residual capacity display pattern specification part 4. Also, the battery residual capacity calculation part 1 has a previous residual capacity usage function 2 for outputting the residual capacity of the battery to the residual capacity display pattern specification part when the remainder of the battery that is calculated by the battery residual capacity part 1 is larger than the residual capacity of the battery that is calculated last time.