The invention provides to make an automatic opening and closing apparatus for a vehicle to be thin. An outer rack is attached to an outer side of a stay fixed to a vehicle in such a manner as to freely move in an axial direction along the stay. A thickness of the stay is set to be smaller than a width, and a cross sectional shape thereof is formed so as to be in a substantially thin convex shape. A width in a base end wall portion of the outer rack is formed so as to be larger than a width of a side surface wall portion corresponding to a thickness of the outer rack, and the outer rack is formed in a substantially thin C cross sectional shape. It is possible to make a thickness of a slide mechanism about a gear with of rack gears lined up in an axial direction in the side surface wall portion by making the width of the side surface wall portion slightly larger than the gear width of the rack gear.