NOVELTY - The structure has a battery side connector (14) that is included with support shafts (15) for supporting battery unit (BU). Engagement recessed portion (27) and vehicle chassis side connector (25) are provided in battery holding block (13). The fitting connection of battery side connector is made at vehicle chassis side connector, while inserting support shaft of battery unit in recessed portion. Battery unit is rotated to fixed position in periphery of support shaft, so that connection fixation of battery unit is performed at battery holding block.    USE - Battery unit connection structure of electric vehicle such as electrically-driven two-wheeled vehicle, three-wheel vehicle and four-wheeled vehicle.    ADVANTAGE - Since battery unit can be rotated by predetermined angle in the periphery of support shaft, the battery side connector is relatively rotated and fixed to battery holding block. The battery side connector is easily connectable with a support shaft, since there is no position shift in vehicle chassis side connector coaxially, hence the mounting operation property of battery unit can be improved. Since the rotation lock of the battery side connector is released, after the fitting connection of the battery side connector is made at vehicle chassis side connector, the continuing battery unit can be rotated smoothly. Since rotation of battery unit can be locked by operation of the key cylinder by an operation key, antitheft of battery unit can be intended by extracting operation key after a lock. The missing prevention from engagement recessed portion and rotation control in the fixed position of battery unit can be performed simultaneously, by the support protrusion in engagement recessed portion.    DESCRIPTION OF DRAWING(S) - The drawing shows the perspective view of the battery unit and battery holding block.    Battery holding block (13)    Battery side connector (14)    Support shaft (15)    Vehicle chassis side connector (25)    Engagement recessed portion (27)    Battery unit (BU)