A method of producing a laminate comprising a polypropylene adhesive layer (I) and a substrate layer (II), the method comprising: a heat treatment step of performing a heat treatment under a temperature condition of 80 to 140°C for 5 to 120 minutes, wherein the laminate satisfies at least the following requirements to : the adhesive layer (I) comprises 97 to 70% by weight of a propylene copolymer (A), and 3 to 30% by weight of a copolymer (B) having a structural unit derived from butene relative to 100% by weight of the total of the copolymer (A) and the copolymer (B), the copolymer (A) has a melting point of 70 to 120°C measured with a differential scanning calorimeter as stated in the description, and includes less than 1 mol % of a structural unit derived from butene, the copolymer (B) has a melting point of 130°C or less measured with a differential scanning calorimeter as stated in the description, and includes 1 mol % or more of the structural unit derived from butene, the adhesive layer (I) comprises a polymer (C) having a structural unit derived from at least one graft monomer selected from the group consisting of unsaturated carboxylic acids and derivatives thereof, and the substrate layer (II) comprises a polyester resin. a heat treatment step of performing a heat treatment under a temperature condition of 80 to 140°C for 5 to 120 minutes, wherein the laminate satisfies at least the following requirements to : the adhesive layer (I) comprises 97 to 70% by weight of a propylene copolymer (A), and 3 to 30% by weight of a copolymer (B) having a structural unit derived from butene relative to 100% by weight of the total of the copolymer (A) and the copolymer (B), the copolymer (A) has a melting point of 70 to 120°C measured with a differential scanning calorimeter as stated in the description, and includes less than 1 mol % of a structural unit derived from butene, the copolymer (B) has a melting point of 130°C or less measured with a differential scanning calorimeter as stated in the description, and includes 1 mol % or more of the structural unit derived from butene, the adhesive layer (I) comprises a polymer (C) having a structural unit derived from at least one graft monomer selected from the group consisting of unsaturated carboxylic acids and derivatives thereof, and the substrate layer (II) comprises a polyester resin. the adhesive layer (I) comprises 97 to 70% by weight of a propylene copolymer (A), and 3 to 30% by weight of a copolymer (B) having a structural unit derived from butene relative to 100% by weight of the total of the copolymer (A) and the copolymer (B), the copolymer (A) has a melting point of 70 to 120°C measured with a differential scanning calorimeter as stated in the description, and includes less than 1 mol % of a structural unit derived from butene, the copolymer (B) has a melting point of 130°C or less measured with a differential scanning calorimeter as stated in the description, and includes 1 mol % or more of the structural unit derived from butene, the adhesive layer (I) comprises a polymer (C) having a structural unit derived from at least one graft monomer selected from the group consisting of unsaturated carboxylic acids and derivatives thereof, and the substrate layer (II) comprises a polyester resin. <EOS>