1. An image forming apparatus comprising: image forming means for forming an image onto a recording medium; a control circuit for controlling operation of said image forming apparatus; a power supply switch for supplying power to said image forming means and to said control circuit when said power supply switch is turned on; a switch, responsive to a position of a door attached to a housing of said image forming apparatus, for permitting power to be supplied to the control circuit regardless of the position of the door, and for cutting off the supply of power to said image forming means when said door is open; measuring means for measuring a density of the image formed on the recording medium; heating means for heating a load by a power supply to the image forming apparatus; detecting means for detecting a temperature of the load which is heated by the heating means, wherein the control circuit executes an image stabilizing control to determine image forming conditions of the image forming means on the basis of the image density measured by the measuring means, and wherein said control circuit controls execution of the image stabilizing control in accordance with an output of the detecting means either when said power supply switch supplies power to said image forming means or when said switch responds to a closed position of the door.