An electric storage unit for a vehicle outside mirror device that electrically rotates a mirror assembly with respect to a vehicle body, the electric storage unit comprising: a shaft fixed to the vehicle body; a gear case rotatably attached to the shaft, the mirror assembly being attached to the gear case; a cover attached to the gear case; and a motor and a rotational force transmission mechanism housed in the gear case and the cover, wherein the gear case has an upright wall surrounding the motor and the rotational force transmission mechanism and an upper portion of the upright wall is open, the cover has a fitting wall fitted from outside onto the periphery of the upper portion of the upright wall and a cover wall covering an opening unit of the upright wall, the upright wall and the fitting wall are provided with a fitting member for assembling the gear case and the cover together, and the fitting member includes a fitting protruding unit provided on the gear case, the fitting protruding unit including an upper inclined surface and a lower horizontal surface an elastically deformable fitting piece provided on the cover and having a first fitting opening into which the fitting protruding unit is fitted, a lower edge of the first fitting opening forming an elastic contact surface that comes into contact with the horizontal surface of the fitting protruding unit such that a portion of the elastically deformable fitting piece elastically deforms downward in a direction of a center line of the shaft when fitted with the fitting protruding unit, characterised in that a portion of the inclined surface of the fitting protruding unit is disposed in the first fitting opening, wherein the lower edge of the first fitting opening has recessed units provided on both the left and right sides of the lower edge and the elastic contact surface is a portion between the recessed units. a shaft fixed to the vehicle body; a gear case rotatably attached to the shaft, the mirror assembly being attached to the gear case; a cover attached to the gear case; and a motor and a rotational force transmission mechanism housed in the gear case and the cover, wherein the gear case has an upright wall surrounding the motor and the rotational force transmission mechanism and an upper portion of the upright wall is open, the cover has a fitting wall fitted from outside onto the periphery of the upper portion of the upright wall and a cover wall covering an opening unit of the upright wall, the upright wall and the fitting wall are provided with a fitting member for assembling the gear case and the cover together, and the fitting member includes a fitting protruding unit provided on the gear case, the fitting protruding unit including an upper inclined surface and a lower horizontal surface an elastically deformable fitting piece provided on the cover and having a first fitting opening into which the fitting protruding unit is fitted, a lower edge of the first fitting opening forming an elastic contact surface that comes into contact with the horizontal surface of the fitting protruding unit such that a portion of the elastically deformable fitting piece elastically deforms downward in a direction of a center line of the shaft when fitted with the fitting protruding unit, characterised in that a portion of the inclined surface of the fitting protruding unit is disposed in the first fitting opening, wherein the lower edge of the first fitting opening has recessed units provided on both the left and right sides of the lower edge and the elastic contact surface is a portion between the recessed units.