To accurately calculate the remaining amount of a tape.

A cassette shell 1 is provided with a memory 13 for storing information indicating the total length of a magnetic tape 11. A tape remaining amount calculator 22 calculates tape lengths wound on a reel 12-1 and a reel 12-2 while assuming that thicknesses are constant, corrects the calculated tape length left being wound on the reel 12-1 on the basis, for example, of the ratio of the sum of the calculated tape length left being wound on the reel 12-1 and the tape length wound on the reel 12-2 to the total length of the magnetic tape 11, and calculates the remaining amount of the magnetic tape 11 to be recorded/ reproduced. The invention is also applicable to a VTR.