An image forming apparatus having a first mode for image forming at a first recorded pixel density and a second mode for image forming at a second recorded pixel density that is higher than that in the first mode, includes: a selector for selecting either the first mode or the second mode; a fixing unit having a temperature detecting sensor to detect a temperature of the fixing unit; and a controller for changing a temperature condition to be set for the fixing unit in accordance with a change between the first recorded pixel density and the second recorded pixel density selected by the selector. When the first mode is changed to the second mode by the selector, the controller controls to switch the temperature condition of the fixing unit from a temperature condition H1 in the first mode to a temperature condition H2 in the second mode lower than that of the temperature condition H1, provides a predetermined second control temperature h2 between the temperature condition H1 and the temperature condition H2 to control inhibiting or allowing an image forming, and controls to inhibit the image forming when a temperature detected by the sensor is higher than the second control temperature h2, and to allow the image forming when the temperature detected by the sensor is lower than the second control temperature h2.