PURPOSE: To form an insulating film having excellent properties on the surface of a grain oriented steel sheet by coating a separating agent for annealing to be coated on the steel sheet in the stage of final secondary recrystallization annealing in a process for producing the grain oriented silicon steel sheet in the form of forming gaps for air permeation.

CONSTITUTION: A grain oriented silicon steel sheet which is cold rolled to a final thickness is subjected to decarburization and primary recrystallization annealing and in succession, a slurry of a separating agent for annealing consisting essentially of MgO is coated thereon and is dried. Such steel sheet is coiled and is subjected to final secondary recrystallization and purification annealing. The separating agent for annealing consisting essentially of MgO is sprayed from nozzles 2 to the silicon steel sheet 1 and is squeezed by wringer rolls 3 and is thus dried in this case. Grooves having a specified depth are formed on the surface of the rolls 3 to coat the separating agent to the layers spaced at ≤40mm gaps (a) and to provide 10W50% difference in the amt. of coating between the part 4 where said amt. is large and the part 5 where said amt. is small. The moisture and gas generated from the separating agent for annealing are escaped through the gaps 4 and 5 in the stage of the final secondary recrystallization annealing, by which the silicon steel sheet having the insulating film having excellent characteristics is obtd.