The control device comprises a vacuum first item of swithchgear (1) which inclusdes a pair of contacts (5,6) that can be separated for interruption purposes. It also includes a main drive shaft (2) for actuating a second item of switchgear (10) immersed in a gaseous insulating fluid (G2) contained at a determined pressure (P2), and further includes an auxiliary shaft (4) to enable a moving contact (5) of the first item of switchgear (1) to be driven. The auxiliary shaft (4) to enable a moving contact (5) of the first item of switchgear (1) to be driven. The auxiliary shaft (4) passes in leaktight manner through a wall (7A, 7") which separates the volume of gaseous insulating fluid (G2) from another volume (V1) of fluid (G1) at a lower pressure, the difference between the respective pressures (P2, P1) of the two fluids (G2,G1) procuring a certain force (Fp) which is applied to siad auxiliary shaft (4) and which participates in said contact pressure force.