A magnetic recording/reproduction apparatus is disclosed which has a first state in which a tape cassette is placed on a chassis and a second state which includes a PLAY mode, a REV mode and a STOP mode. The apparatus comprises: a reel base rotatably mounted on the chassis via a shaft and engaging with a reel which holds the magnetic tape wound thereon in the tape cassette; a tension post allowing the magnetic tape to pass around a periphery thereof in the second state; and a tension arm supporting the tension post at a fixed position of the tension arm, the tension arm being swingably mounted on the chassis, the reel base including a drum portion rotating integrally with the reel base. The apparatus further comprises: a tension band having a center portion passing around the drum portion and one end swingably held by the tension around the arm; and a tension band regulating arm movably supported by the chassis, the tension band regulating arm holding the other end of the tension band. When the magnetic tape runs in a forward direction in the PLAY mode, the tension band permits the apparatus to control the tension of the magnetic tape, and when the magnetic tape runs in one of the second state modes, the tension band regulating arm moves to a position at which the tension band is loosened and the tension arm is fixed in a first position as in the PLAY mode.