Patent ID: 8873980

Claim:
A developing device comprising: a development roller which carries a toner and which is opposite a photoconductor drum; a magnetic roller which is arranged opposite the development roller and which performs, with a magnetic brush, supply of the toner to the development roller and separation of the toner from the development roller; a transformer which generates an alternating-current voltage applied to the development roller; a switching portion which passes and interrupts a current to the transformer; an output control portion which stepwise changes, between sheets when sheets are continuously printed, from a first duty ratio to a second duty ratio, a duty ratio in switching by the switching portion a plurality of times; and a capacitor in which one end is connected to the transformer and the other end is connected to the switching portion, wherein the output control portion changes the duty ratio from the first duty ratio to the second duty ratio at divided widths in which no magnetic saturation is produced in the transformer while a predetermined time period is being acquired, a number of steps from the first duty ratio to the second duty ratio is equal to or more than five but is equal to or less than twenty when the duty ratio in the switching is changed from the first duty ratio to the second duty ratio, and the predetermined time period is a few milliseconds.