A belt member driving device includes an arm configured to be movable with movement of a belt member in a width direction thereof while being in contact with an end of the belt member in the width direction thereof, a first detected portion provided on the arm, a second detected portion provided on the arm and disposed in a position different from that of the first detected portion in a direction perpendicular to a movement direction of the arm on a plane where the arm is moved, a first sensor configured to detect the first detected portion, and a second sensor configured to detect the second detected portion. The second sensor and the first sensor partly overlap each other in the movement direction of the arm as viewed in a direction perpendicular to the movement direction of the arm.