An image forming unit includes: an image carrier on which a latent image is formed; an intermediate transfer belt to which a toner image obtained by developing the latent image on the image carrier is transferred; plural rolls, around which the intermediate transfer belt is wrapped and stretched; and a pair of side frames for rotatably supporting the plurality of rolls. Each of the side frames includes a guide groove for guiding a shaft of at least one of the plural rolls through an opening which is open in a direction orthogonal to an axial direction of the plural rolls.