IMAGE FORMING APPARATUS

PURPOSE:To reduce the cost of an image forming apparatus by changing the operating condition f an automatic exposure sensor so as to actuate the sensor also as a copy detecting sensor. CONSTITUTION:Light radiated from the light emitting portion of an automatic exposure(AE) sensor 5 which detects copy density is applied to a copy and the reflected light is received by a light receiving portion. The quantity of the reflected light is received with the density of the copy and the output is varied accordingly. When signals for turning transistors Tr 1 and Tr 2 on are applied to respective terminals 1, 2 at a set value changing device 6 the gain 1 and the reference value of a set value for AE are selected. When signals for turning the transistors Tr 1, Tr 2 off are applied to the respective terminals 1, 2 the gain 2 and the reference value of a set value for copy detection are selected. The sensor for detecting copy density is thus used also as a sensor for detecting copies by changing the operating condition of the sensor.