An image fixing unit for a wet image forming apparatus comprises a fixing section and a preheating means. The fixing section has a first fixing roller, and a second fixing roller which rotates in close contact with the first fixing roller to feed paper through a gap (a fixing nip) between the first and second fixing rollers. The preheating means is disposed on a feed path of the paper before the paper enters the fixing nip, and comes into contact with a non-image surface of the paper to allow the image to be exposed to the air. Either one of the first and second fixing rollers is disposed to bring a surface thereof into contact with the non-image surface of the paper before the paper passes through the fixing nip, and the fixing roller brought into contact with the paper has a heating element mounted therein.