To reduce variation in a tension of a timing belt, to eliminate a delaying element on controlling and to prevent a control performance from being lowered for a long time in a drive transmission mechanism for conveying a recording medium by using the timing belt and reciprocating a recording head.

In the drive transmission mechanism for driving the recording head or the like, a shaft 3a of a driving pulley 3 having the timing belt 5 suspended thereto is slidably supported by a body side of an image forming apparatus and a shaft 4a of a follower pulley 4 is fixed to the body of the apparatus. As the shaft 3a is pulled to the body side by a tensile spring 6 (a tension control mechanism), the tension of the timing belt 5 is adjusted to be constant. A stopper 7 for restricting the movement of the shaft 3a is provided as a restricting member and the timing belt 5 is applied with the constant tension. Only when the driving pulley 3 moves by a predetermined amount or more, the shaft 3a is brought into contact with the stopper 7, and then the movement of the driving pulley 3 is restricted.