To realize joining of transparent bodies under the condition that the production cost of a joined body is checked, its transparent feeling is kept and it has an enough joint strength by a method wherein transparent bodies made of amorphous polyethylene terephthalate are heat-fused after the joining surfaces of the transparent bodies are corona-discharge-treated.

A joined body is a card case 1 consisting of two sheets of plate material 2 and 3 and muntins 4, 5 and 6 arranged between three sides of the peripheral edge of the two plate materials. These plate materials 2 and 3 and the muntins 4, 5 and 6 are transparent amorphous polyethylene terephthalate films cut respectively in the predetermined shapes. Respective joining surfaces 2a, 3a, 4a, 4b, 5a, 5b, 6a and 6b are corona-discharge-treated. Next, successively the plate materials 2 and 3 and the muntins 4, 5 and 6 are quickly set to a lower mold 7, in which the accepting electrode 10 of a high frequency welder 8, so as to be pressed by the pressing electrode 14 of an upper mold 13 in order to apply a high frequency voltage between the electrodes 10 and 14, resulting in heat-fusing the plate materials 2 and 3 and the muntins 4, 5 and 6.