To arrange a key on a corner part of a first case of a terminal device.

The portable terminal device 1 includes the first case 2, and the key 10 mounted on a cut part of the corner part of the first case 2. The portable terminal device 1 also includes a key support part 20, which includes a shaft part having a rotary axis in a side surface direction of the corner part and mounted on a bearing part formed on the first case 2, and a peripheral part hung on a peripheral edge of the cut part of the first case 2, and supports the key 10. The terminal device 1 further includes: a transmission part 30 for transmitting pressing force through the key support part 20 to a predetermined part of a substrate when predetermine pressing force is applied on the key 10 in a rotation direction determined by the rotary axis; and a second case for housing the transmission part 30, the substrate 6, and a switch by being combined with the first case 2 mounting the key 10 and the key support part 20.