An image forming apparatus has a black sensitized body and plural color sensitized bodies arranged in a row as well as a belt adapted to move round on a course, sequentially passing by or coming into contact with the plural sensitized bodies, of which the black sensitized body is located at an end of the row, a roll for causing the belt to come into contact with the black sensitized body and a retractable roll located between the color sensitized body disposed at the other end of the row of the sensitized bodies opposite to the black sensitized body and the color sensitized body immediately adjacent to the black sensitized body and adapted to shift from a position for holding itself in contact with the belt to a position for separating itself from the belt and vice versa to change the course of round movement of the belt.