Patent ID: 8437650

Claim:
An image forming apparatus comprising: an image carrier; an image forming section which forms a toner image onto the image carrier; a sensor which detects a density of a patch image which is formed on the image carrier; an image quality control section which controls an image forming condition based on a detection value of the sensor; and a judging section which judges whether the detection value of the sensor has a tendency of increasing or decreasing with a passage of time by determining whether each detection value is higher than a previous detection value, or by determining whether each detection value is lower than the previous detection value, or by determining the tendency of increasing or decreasing based on a plurality of detection values with the passage of time when an inclination of an approximately straight line fit to the plural detection values is different from an inclination of an approximately horizontal line; wherein, the image quality control section compensates the image forming condition with a first compensating coefficient representing a ratio of a difference between the detection value and a reference value to a compensation amount in a case when the judging section judges that the detection value does not have the tendency of increasing nor decreasing, and compensates the image forming condition with a second compensating coefficient of which absolute value is larger than an absolute value of the first compensating coefficient corresponding to the second compensating coefficient, in a case when the judging section judges that the detection value has the tendency of increasing or decreasing.