The invention concerns a driving device for locking and unlocking a lock with conditional opening, comprising: motoring means (MT) including a driving element (36) with a rotation axis (X1); a transmission arm (26) mounted about a rotation axis (X2), separate from the axis (X1); a locking unit (PVI) connected to the arm (26) and capable of taking up an active position (P1) countering the displacement of a rod, and an inoperative position (P2) allowing its displacement; and elastic means (48) to activate the locking unit (PVI) when its movement is blocked by the rod. The invention is characterised in that the elastic means (48) are arranged between the driving element (36) and the transmission arm (26), said elastic means (48) being in direct driving contact with a surface connected (54) to the transmission arm (26). Said device is in particular applicable to a lock with conditional opening, in particular a time lock.