treating may be performed by moving the local heater 60 in a direction from a side to another side of the substrate 10 included in the sample 50 e g in a direction from a left side to a right side of fig5 and 6 the second part a 2 may be a part adjacent to the first part a 1 in the direction in which the local heater 60 moves from the first part a 1 the method of producing the monocrystalline graphene layer according to an embodiment of the present invention has been described above with reference to the drawings the present invention does not disclose a method of directly growing monocrystalline graphene using a hydrocarbon gas but discloses a multistage method of growing polycrystalline graphene on a substrate using a hydrocarbon gas forming a catalyst on the polycrystalline graphene and then recrystallizing the polycrystalline graphene into monocrystalline graphene by heat treating the polycrystalline graphene and the catalyst using a zone heating scheme the heat treating may be understood as post annealing one of factors considered to produce a monocrystalline graphene layer is temperature a temperature for producing bulk graphite is equal to or greater than about 2500k in consideration of the size of carbon atoms and bonding between carbon atoms.