A structure of a panel which can be thinned down to about a panel thickness of a PDP and a manufacturing method thereof are provided. A gas filling hole is provided to a surface of a rear glass substrate of a PDP, the surface coming in contact with a front glass substrate of the PDP. Vacuuming and filling of a discharge gas are performed through the gas filling hole. After filling of the discharge gas, a mechanism for lifting solder iron up and down and supplying solder provided inside a chamber inserts a tip of an ultrasonic soldering iron into the gas filling hole to start supplying a solder which is a material for a plug sealant. When a series of forming steps of the plug sealant are finished, the ultrasonic soldering iron is retreated before the solder is solidified to finish formation of the plug sealant.