An image forming apparatus an image bearing member adapted to bear a toner image and having a first glossiness in a first direction and a second glossiness lower than said first glossiness, and an optical detection unit including a light-emitting unit and a light-receiving unit, wherein a light emitted by the light-emitting unit is reflected by the image bearing member and is received by the light-receiving means and an optical direction from the light-emitting means to the light-receiving means is substantially same as the first direction of the image bearing member.