A method includes a supporting step supporting first planar surfaces of two substrates 20A and 30A having flexibility with supporting boards 50 and 60 each having flexibility and a larger thickness than the two substrates 20A and 30A, a thin film pattern formation step, after the supporting step, forming a thin film pattern on second planar surfaces of the two substrates 20A and 30A, a bonding step, after the thin film pattern formation step, bonding the two substrates 20A and 30A at surfaces each having the thin film pattern thereon with the sealant therebetween to form a bonded substrate 70, a first curving step, after the bonding step, curving the bonded substrate 70 while curing the sealant, a detachment step, after the first curving step, detaching the supporting boards 50 and 60 from the bonded substrate 70, and a second curving step, after the detachment step, further curving the bonded substrate 70.