An image forming apparatus includes an opening/closing member that pivots with respect to an apparatus main body between a closed position and an open position, a lock mechanism that holds the opening/closing member in the closed position, and a detection member that detects a position of the opening/closing member. The lock mechanism includes a first engaging portion and a second engaging portion at both ends of the apparatus main body, and a first engaged portion and a second engaged portion at both ends of the opening/closing member, in an axial direction. An engagement width for the second engaging portion and the second engaged portion is large compared with that of the first engaging portion and the first engaged portion, when the opening/closing member is in the closed position and locked by the lock mechanism. The detection member is located close to the second engaging portion in the axial direction.