To provide a composition of a magnetic medium drive, having a low cost and good processability, excellent in mechanical strength, and reduced in the total amount of gas generated, and a composition for forming it.

The composition for forming a component of a magnetic medium drive contains a fluororubber and an EPDM, and gives a total amount of outgassing of at most 1 μg/g. The mass ratio of the fluororubber to the EPDM is (30:70) to (90:10). It is desirable that the fluororubber comprises a ternary fluororubber consisting mainly of tetrafluoroethylene(TFE), hexafluoropropylene(HFP) and vinylidene fluoride(VdF), or a binary fluororubber consisting mainly of hexafluoropropylene(HFP) and vinylidene fluoride(VdF), wherein (1) the mass ratio of vinylidene fluoride to hexafluoropropylene is (30:70) to (70:30), and (2) the content of tetrafluoroethylene is 0-50 mass pts. based on 100 mass pts. of the total of two components described in (1).