A rotary cylinder device for helical scan type magnetic recording/reproducing apparatus including a rotary cylinder having an axis of rotation arranged in opposition a stationary cylinder in the direction of the axis of rotation with a small gap therebetween. The rotary cylinder has an end surface facing the stationary cylinder and an outer peripheral surface, recesses formed in the end surface and opening in the outer peripheral surface so as to extend therefrom radially inwardly over a small distance. Each of the recesses has a leading end wall and a trailing end wall, as viewed in the direction of rotation of the rotary cylinder. Magnetic heads are fixed to the rotary cylinder and are positioned in the recesses and have outer extremities projecting beyond the outer peripheral surface of the rotary cylinder. The distance between the leading end wall and the trailing end wall of each recess progressively decreases towards the axis of rotation of the rotary cylinder so that the distance is greatest at the outer end of the recess adjacent the magnetic head and the smallest at the inner end of the recess remote from the magnetic head.