Recording and/or reproducing apparatus having rotary drum unit

A recording and/or reproducing apparatus for recording and/or reproducing information on or from a tape-shaped recording medium, comprising:

• a) a head arranged to record and/or reproduce information on or from the tape-shaped recording medium;
• and
• b) a rotary drum having said head mounted thereon and having an outer peripheral surface around which the recording medium is wrapped, said outer peripheral surface having a plurality of grooves formed surrounding said outer peripheral surface, said outer peripheral surface including at least two first outer peripheral surfaces and at least one second outer peripheral surface which has a smaller diameter than that of said first outer peripheral surfaces, each of said at least one second outer peripheral surface being sandwiched respectively in between said first outer peripheral surfaces, each of said plurality of grooves being sandwiched in between one of said first outer peripheral surfaces and said second outer peripheral surface, and the length of said first outer peripheral surfaces and the length of said second outer peripheral surface in the direction of an axis of rotation of said rotary drum are equal to each other, whereby a first air film thickness between said recording medium and said rotary drum on a recording medium entrance side of said rotary drum is substantially the same thickness as a second air film thickness on a recording medium exit side of said rotary drum.