To provide an ink jet image forming apparatus performing recording by reciprocating a carriage mounting an ink jet recording head in which an image can be formed with high image quality by sustaining positional relation between an ink ejection nozzle and a scanning (guide) shaft with high precision.

Image recording is carried out by reciprocating a carriage 1 mounting an ink jet head 2 (21-24) along a scanning shaft 3. One end 3b of the scanning shaft 3 is secured to the side plate 11 of the apparatus body, an opening 12a allowing insertion of the carriage 1 is provided in the opposite side plate 12 of the apparatus body, and the other end 3a of the scanning shaft 3 is supported by a fixing plate 13 which can be fixed removably to the opposite side plate 12 through a screw 14, or the like. The ink jet head 2 is installed removably from one end 3a of the scanning shaft 3 while being mounted on the carriage 1.