The optical apparatus accessory includes multiple terminal faces arranged in a direction of a relative movement for attachment to an optical apparatus and allowed to make contact with multiple terminal pins provided in the optical apparatus, and electric insulation portions provided between each two adjacent terminal faces. The multiple terminal faces are arranged at a same height, each of the electric insulation portions includes two adjacent-to-terminal potions respectively adjacent to the two adjacent terminal faces and a convex portion provided between the two adjacent-to-terminal potions and having a higher height than that of the two adjacent-to-terminal potions. The two adjacent-to-terminal potions have a height same as or lower than that of the terminal faces, and the convex portion has a height same as or higher than that of the terminal faces.