1. An image forming apparatus comprising: a reference-pattern detecting transfer-body to which a reference pattern image formed on an intermediate transfer body is transferred directly without a recording material, the reference-pattern detecting transfer-body arranged opposite to an intermediate transfer body in a secondary transfer unit in which images formed on a plurality of image carriers are transferred onto the intermediate transfer body, and an image formed on the intermediate transfer body is transferred onto the recording material; a reference-pattern detecting unit that detects the reference pattern transferred onto the reference-pattern detecting transfer-body; and a condition changing unit that changes conditions for forming an image based on a result of detection by the reference-pattern detecting unit.