IMAGE FORMING DEVICE

PROBLEM TO BE SOLVED: To detect the positions of images for detecting positions respectively formed by plural toner image forming devices and transferred on the front surface side of a belt by an inexpensive image position sensor whose constitution is simple. SOLUTION: The images Py, Pm, Pc and Pk for detecting the positions of respective colors Y, M, C and K are constituted so as to be provided with two line segments Y1 and Y2 arranged by being mutually inclined at positions separated in a sub-scanning direction Z. In this case, the image position sensor SN1 detecting the quantity of light reflected from one reflected light quantity detection point set along the carrying path of the image transferred on the belt B and a main scanning direction writing start position deviation amount calculation means calculating deviation amount between the actual positions of the main scanning direction X of the images Py,... calculated based on a gap between the detecting positions of two line segments Y1 and Y2 in the sub-scanning direction Z and a target position in the main scanning direction.