An image forming apparatus includes a first unit dismountably mounted on a main body frame and a locking mechanism releasably holding the first unit mounted. The locking mechanism has a handle portion, a lock member, and a preloading member. The handle portion is on the first unit, and is movable to and fro in the mounting and dismounting directions of the first unit. The lock member is swingably on the first unit, and has a hook portion engageable with an engaged portion formed on the main body frame. The preloading member preloads the lock member in a first direction in which the hook portion engages with the engaged portion. As the handle portion is moved in the dismounting direction, the lock member swings in a second direction opposite to the first direction against the preloading force of the preloading member to disengage the hook portion from the engaged portion.