A welding device includes a first graphite heater and a second graphite heater that come into contact with a first member and a second member; and a first die and a second die, which sandwich the first and second graphite heaters with the first and second members interposed therebetween. The first and second graphite heaters have graphite sheets that generate heat by electric power, insulating materials, outer covers, and inner covers, and are configured such that structures of the graphite sheets covered by the insulating materials are interposed between outer covers and inner covers.