Variable bulge device for rotatable head drum

A variable bulge device for displacing bulges of a rotation head drum, capable of adjusting a protruded amount of a bulge used, depending on a rotation speed of the rotating head drum and the kind of a tape used. The device includes an operating member partially protruded at one end thereof through a bulge hole formed at a lower drum of the rotation head drum, the operating member having a variable bulge provided by the protruded end, and a drive unit for driving the operating member and thereby adjusting the protruded amount and position of the variable bulge. For adjusting a protruded amount of a bulge used, depending on a rotation speed of the rotating head drum and the kind of a tape used, the device includes a hollow elastic rubber film partially protruded at an upper end thereof through a bulge hole formed at a lower drum of the rotation head drum, the elastic rubber film having a variable bulge provided by the protruded end, an operating fluid contained in the elastic rubber film, an operating fluid expanding unit adapted to expand the operating fluid and thereby adjust the protruded amount of the variable bulge.