Abstract: A deck mechanism for a magnetic recording/reproducing apparatus comprises a main deck provided with a head drum and a capstan motor; a sub-deck installed on the main deck to be loaded/unloaded, the sub-deck being provided with a pair of reel discs, onto which tape reels of a tape cassette are seated; a pole base loading unit for taking out and guiding a tape to be in contact with a side of the head drum when the sub-deck is loaded and guides; a pinch roller unit for compressing the tape against a spindle of the capstan motor when the sub-deck is loaded; a brake unit for selectively braking one of the roll discs; a main sliding member mounted on the main deck to be capable of reciprocatingly sliding, the main sliding member controlling the driving of the pinch roller unit; and a main cam gear mounted on the main deck to be capable of rotating, the main cam gear causing operating all of the sub-deck, the pole base loading unit, the brake unit, and the main sliding member to perform linked movements while the ma