An image forming device continuously forming an image according to a job in a conveying direction of along continuous paper includes: an image formation section forming the image according to the job on the continuous paper; an interval setting section setting a job interval of the image according to the job, which is continuously formed by the image formation section, on the basis of an operation from a user; an image forming process switching section switching two states of a state where the image formation section forms a color image and a state where the image formation section forms a monochromic image; and a switching determination section determining whether or not the two states are switched on the basis of a comparison result between the job interval set by the interval setting section and a paper conveying distance according to a switching time required for switching the two states.