[Problem] To allow combining devices having different functions according to an application, and improve convenience for a user. [Solution] Provided is an information terminal device, comprising: a terminal for mounting (1) in which belt members (4a, 4b) may be respectively coupled to both end parts of an external case (10) provided with a display unit (131) on the upper face； and a dock device (2) which is detachably engaged with the bottom part of the external case (10) of the terminal for mounting (1), and is electrically connected to the terminal for mounting (1) via a dock-side connection terminal (21). The terminal for mounting (1) and the dock device (2) are provided with a function which carries out transmission and receiving of data to be displayed on the display unit (131) via the dock-side connection terminal (21).
