A film supply apparatus comprising: two film holders (2a, 22b) supporting two rolls of film (101, 100) as a film on a use side and a film on a stand-by side, respectively; a feed roller for feeding the film on the use side; a film holding member releasable holding a leading end portion of the film on the stand-by side in the upper stream of the feed roller in a feeding direction of the film such that the film on the stand-by side is drawn out to face the film on the use side; a film returning mechanism placed upstream of the film holding member in the feeding direction of the film and pulling back the film on the stand-by side upstream in the feeding direction of the film in a state in which the film returning mechanism holds the film on the stand-by side in the upper stream of a part held by the film holding member; and characterised by a fusion bonding mechanism placed between the film holding member and the film returning mechanism in the feeding direction of the film, the fusion bonding mechanism has a heater bar containing an electric heater, and a heater bar receiver placed opposite to the heater bar, the heater bar reciprocates in a direction to pressurize the heater bar receiver or move away from the heater bar receiver, and the heater bar and the heater bar receiver are formed such that they cooperate to pressurize and heat the film for heat-sealing the two opposite films throughout a width thereof, and wherein the heater bar and the heater bar receiver performs the heat-sealing of the films (101, 100) on the use side and the stand-by side in a state in which the leading end portion of the film on the stand-by side released from the holding by the film holding member is pulled back by the film returning mechanism to be placed in an area pressurized by the heater bar and the heater bar receiver and a trailing end portion of the film on the use side is fed by the feed roller to overlie the film on the stand-by side in the area pressurized by the heater bar and the heater bar receiver. two film holders (2a, 22b) supporting two rolls of film (101, 100) as a film on a use side and a film on a stand-by side, respectively; a feed roller for feeding the film on the use side; a film holding member releasable holding a leading end portion of the film on the stand-by side in the upper stream of the feed roller in a feeding direction of the film such that the film on the stand-by side is drawn out to face the film on the use side; a film returning mechanism placed upstream of the film holding member in the feeding direction of the film and pulling back the film on the stand-by side upstream in the feeding direction of the film in a state in which the film returning mechanism holds the film on the stand-by side in the upper stream of a part held by the film holding member; and characterised by a fusion bonding mechanism placed between the film holding member and the film returning mechanism in the feeding direction of the film, the fusion bonding mechanism has a heater bar containing an electric heater, and a heater bar receiver placed opposite to the heater bar, the heater bar reciprocates in a direction to pressurize the heater bar receiver or move away from the heater bar receiver, and the heater bar and the heater bar receiver are formed such that they cooperate to pressurize and heat the film for heat-sealing the two opposite films throughout a width thereof, and wherein the heater bar and the heater bar receiver performs the heat-sealing of the films (101, 100) on the use side and the stand-by side in a state in which the leading end portion of the film on the stand-by side released from the holding by the film holding member is pulled back by the film returning mechanism to be placed in an area pressurized by the heater bar and the heater bar receiver and a trailing end portion of the film on the use side is fed by the feed roller to overlie the film on the stand-by side in the area pressurized by the heater bar and the heater bar receiver.