PROBLEM TO BE SOLVED: To provide a film welding method by which a resin film can be sealed reliably, efficiently and stably to a container formed of foamed resin.SOLUTION: A method for welding a resin film 13 to a container 11 formed of a foamed resin having a buckling strength of 3.0 to 30.0 kgf is provided. A welding temperature is set in 80 to 240°C. Pressure when the resin film 13 is pressed against the container 11 is set at 1.0 to 6.2 kgf/cm.