A user input apparatus according to the present invention is configured like a wrist watch and a system can recognize the gesture such as "grip" and "release" or the like and can input the gesture as a command merely by attaching the user input apparatus to user's wrist. Further, by adding an acceleration sensor or the like for measuring the movement of an arm itself to a bracelet, the user input apparatus can be configured so as to input more complicated instruction and command. The user input apparatus can be used as an input apparatus for a wearable computer (or wearable computer), or a controller to input a command for a game machine or the like.