NOVELTY - The battery unit has a case (15) that is comprised on a bottom face (11) and two slopes (14) respectively formed by mutually equal length from the both ends at the bottom face. A cylinder-shaped cell (16) is accommodated in the inside of the case. The length (L3) of slope of the case is smaller than length (L4) of the bottom face by arranging the cell along the bottom face in bigger pitch (P2) than outer-diameter (D1) of the cell.    USE - Battery unit mounted in electric vehicle (claimed) such as electrically-driven two-wheeled vehicle. Can also be used in saddle riding type three-wheeled vehicle and saddle riding type four-wheeled vehicle.    ADVANTAGE - Since the length of the slope of the case can be made smaller than the length of bottom face, the height from bottom face to the intersection of two slopes can be made small, and the height dimension of battery unit can be made small, so that the accommodation space of battery unit can be reduced significantly. The bottom face can be located in vehicle main portion center side along perpendicular line, so that the vehicle width direction dimension of battery unit becomes small, and the bulging to the vehicle width direction of side cover can be suppressed. Since the battery unit can be supported by the rear frame and sub-frame, the battery unit can be integrated with vehicle main portion, and the battery unit can be maintained reliably. The inclined surface of step side cover bulges to vehicle main portion outward can be suppressed, the storing capacity of battery can be secured within a bank angle. Since the attachment or detachment cover can be removed, the battery unit can be easily taken out from the inside of the step side cover.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for an electrical vehicle.    DESCRIPTION OF DRAWING(S) - The drawing shows the schematic views showing configuration regarding the length of the bottom face of case and the length of slope in battery unit. (Drawing includes non-English language text)    Bottom face (11)    Slopes (14)    Case (15)    Cell (16)    Outer diameter of cell (D1)    Length of slope (L3)    Length of bottom face (L4)    Bigger pitch (P2)