A portable terminal device, capable of improving the releasing property of fitting pieces of an upper case and a lower case at the time of disassembling the appliance, and lowering generation of deformation or crack of the main body by bend or twist while maintaining a sufficient fitting holding force. In the main body of the portable terminal device, a plurality of fitting pieces are provided each in an upper case and a lower case for holding and fixing with each other. The fitting pieces have a fitting horizontal surface to be substantially parallel for holding with each other when the upper case and the lower case are engaged. A part of the fitting horizontal surface of the fitting pieces of at least one of the upper case and the lower case has a fitting twisted surface twisted in the direction away from the fitting horizontal surface of the other fitting piece in the fitting pieces. In releasing the fitting pieces of the upper case and the lower case at the time of disassembling the main body in the portable terminal device having the configuration, the fitting piece without the fitting twisted surface is gradually released along the fitting twisted surface of the fitting piece having the fitting twisted surface.