The invention relates to a tape sage preventing apparatus for a tape playing machine such as a video tape recorder wherein the tape can be prevented from sagging during a reversal of the direction of tape transport. 
In general, as shown in FIG.  1, a video tape recorder which can record and/or reproduce signals to and from a magnetic video tape 4 using a rotary head drum 2 transports the tape along a predetermined running path.  In such a tape recorder, when, for example, the transport direction of the tape is changed from the forward direction to the reverse direction, a supply reel disk 3 rotates temporarily in the forward direction, and thereafter rotates in the reverse direction.  At this time, the tape sags, i.e., loses tension, because the reel disk 3 continues to rotate due to its rotational inertia in the forward direction, arrow j, even though it is braked by a sub-brake 6. 
For this reason, to prevent the aforementioned tape sag, when the direction of transport of the tape 4 is changed from forward direction to the reverse direction, a tension bar 5 (FIG.  2) moves from the position designated by the solid line to the alternative position indicated by the long and short dashed line, see FIG.  2, to absorb the tape sag.  However, tape 13 still released in the initial forward direction during the change of transport direction because the tension applied to the tape in forward direction (the tension bar 5 being in the state indicated by the solid line) is larger than the brake force that the sub-brake 6 can generate.  Furthermore, because an amount of the tape corresponding to one frame is added, the tension bar can not absorb all of the released tape, so that the tape sag still occurs. 
The aforementioned tape sag means that the tension in the tape is lowered and that the contact force between the drum head and the tape is correspondingly decreased causing noise to appear on the TV screen. 
An alternative method of preventing tape sag is to increase the baking force of the sub-brake.  However, the torque is then reduced during the reverse search and the rewind functions, so it is different to apply such a method to the tape recorder.