In a magnetic recording/reproducing apparatus of the helical scanning type the rotation speed of the reels in operation is detected and it is judged to be abnormal, if the rotation speed exceeds the upper limit thereof. This upper limit can be varied, depending on various operating modes. When an abnormality is detected, the brake of the reels is driven and the rotation of the drum is stopped. After the tape has been stopped, the tape is unloaded while rotating the supply side reel and the take-up side reel, the drum remaining not rotated.