In an image forming apparatus using an optical sensor for detecting light reflection characteristics of a toner image fixed on a transfer material, occurrence of gloss unevenness in a printed image can be prevented. The image forming apparatus includes a first transfer material conveying path for normal printing, a second transfer material conveying path for image density control, a sensor contact member integral with the optical sensor and a transfer material supporting member contacting a transfer material rear surface in a position opposing the sensor contact member. At the time of normal printing, the sensor contact member and the transfer material supporting member are disposed in a spaced position against the transfer material, and at the time of image density control, the sensor contact member or the transfer material supporting member moves so that the sensor contact member and the transfer material supporting member contact the transfer material.