The Pole was quickest on all four Friday stages of the French rally, driving the same Citroen C4 WRC that he used to win in Como last weekend.
Kubica's main rival, former World Rally Championship and Intercontinental Rally Challenge frontrunner Freddy Loix, is already 1m25s behind in his Peugeot 307 WRC in slippery conditions.
The rally continues until Sunday.
Kubica said after his Como win that he was keen to challenge himself on increasingly demanding rallies as he adapted to the Citroen World Rally Car.
He has been making a tentative motorsport comeback in domestic rallies this year as he continues his rehabilitation from the severe injuries that halted his Formula 1 career in February 2011.