To prevent image defects caused by the presence or absence of humidification to a sheet.

An image forming apparatus comprises: a first image forming part for forming a first image on an image carrier and transferring the first image to a sheet; a sheet humidification part for humidifying at least the sheet having the first image transferred thereto; a humidification switch part for switching the presence or absence of humidification to the sheet by the sheet humidification part; a second image forming part for forming a second image on an image carrier and transferring the second image to the sheet; a conveyance part for conveying the sheet from the first image forming part to the second image forming part; and a control part for controlling the first and the second image forming parts. The control part switches an image formation control at the second image forming part in accordance with the presence or absence of the humidification to the sheet by the sheet humidification part, thereby preventing image size troubles and image defects.