Abstract: A Venetian blind includes two string reels, two spring reels, a leaf spring and a wheel set. The string reels are engaged with each other. The spring reels engaged with each other. The leaf spring includes two sections respectively wound on the spring reels so that one of the sections of the leaf spring gets longer and the remaining one of the sections of the leaf spring gets shorter when the spring reels are rotated. The wheel set connects one of the string reels to one of the spring reels. None of the spring reels is engaged with any of the string reels without the wheel set.