Image forming apparatus

An image forming apparatus comprising:

• a density sensor which measures a density of an image formed on a paper or a toner deposition amount, and outputs a measured value;
• a periodic unevenness detector which detects a periodic unevenness as a density unevenness which periodically appears on the image in a carrying direction of the paper, and calculates a period of the periodic unevenness based on the image density or the toner deposition amount output from the density sensor;
• a causal member identifying section which identifies a causal member as a cause of the periodic unevenness based on the period of the periodic unevenness detected by the periodic unevenness detector;
• and
• a judgement section which judges whether or not the periodic unevenness is transient based on information of the causal member identified by the causal member identifying section, information of at least one of a resting time in which the image forming apparatus has been left inoperative, an operating time of the causal member, and an image forming condition for forming the image, and information of a temperature and a humidity inside the image forming apparatus.