A tape rewinding mechanism for a magnetic recording/reproducing apparatus is disclosed in which, when ejecting the tape from the deck, the reel with the tape installed thereon is driven by a capstan motor, so that the tape can be recovered with a proper tension maintained between the tape and the drum, thereby preventing damage to the tape. A driving gear is installed on a lever of a transmitting gear which is meshed with the capstan gear, and thus, the take-up reel is driven during loading, while the supply reel is driven during an unloading. During a reproduction, the take-up reel and the supply reel are easily driven by the transmitting gear, thereby simplifying the structure of the deck.