A primer (16) for forming a resin frame (17) is formed on an outer end portion (16p) of a separator (1) of a fuel cell. An electrodeposition coating device (2) includes an upper frame (21) and a lower frame (22), and covers only the outer end portion (16p) of the substrate (11) with a center portion (12) of the substrate (11) left uncovered. When the substrate (11) is sandwiched between the upper frame (21) and the lower frame (22) of the electrodeposition coating device (2), an annular electrodeposition chamber (31) is formed with the outer end portion (16p) of the substrate (11) located in the electrodeposition chamber (31). Then, the electrodeposition chamber (31) is filled with an electrodeposition coating solution (32), and electrodeposition coating is performed. Then, cleaning is performed by using purified water, and drying is performed by using hightemperature air.