An image forming apparatus includes a housing including a cover configured to cover an opening provided in the housing, a transfer unit configured to move a loop-shaped moving member, a portion of which, across an entire width in a direction perpendicular to a moving direction thereof, being exposed through the opening when the cover is opened, and a sensor unit including a holding member configured to hold a plurality of optical sensors arranged in a direction perpendicular to the moving direction of the loop-shaped moving member and configured to detect detecting respective amounts of light at respective areas different from each other on the loop-shaped moving member, end portions of the sensor unit being fixed in the housing at end portions of the opening in a widthwise direction perpendicular to the moving direction of the loop-shaped moving member.