The image forming apparatus forms an image on a recording medium by using an ink and an aggregating treatment agent. The ink contains coloring material, and the aggregating treatment agent contains a component which causes the coloring material to aggregate. The image forming apparatus includes: a treatment liquid deposition device which deposits a treatment liquid onto the recording medium, the treatment liquid containing the aggregating treatment agent; a treatment liquid heating device which heats the treatment liquid having been deposited on the recording medium to form a solid or semi-solid layer of the aggregating treatment agent on the recording medium; a treatment liquid permeation suppression device which suppresses permeation of the treatment liquid into the recording medium at least from a time of deposition of the treatment liquid onto the recording medium until formation of the solid or semi-solid layer of the aggregating treatment agent; and an ink droplet ejection device which ejects and deposits droplets of the ink onto the recording medium on which the solid or semi-solid layer of the aggregating treatment agent has been formed.