A rotary magnetic head cylinder device for use in a helical-scanning system video tape recorder has a projection provided on a tape running race of a stationary lower cylinder near a location at which a magnetic tape leaves from the lower cylinder. The projection is preferably integral with the tape running race and has a small area which is defined by a shoulder circumferentially extending identically with a tape guide shoulder contouring the lower edge of the tape running race and which spreads perpendicularly to the tape running race, and an upper surface coplanar with the top face of the lower cylinder, and a height defined by a protruded length radially outwardly toward the outer circumferential surface of the lower cylinder. The projection serves to reduce vibrations of the magnetic tape generated when the video head carried by the rotary upper cylinder leaves from the magnetic tape.